View source for Allies of World War I

{{Short description|Military coalition in World War I}}
{{EngvarB|date=April 2021}}
{{Use dmy dates|date=February 2024}}
{{Infobox geopolitical organization
| conventional_long_name = {{hlist|Allied Powers|Entente}}
| common_name            = Entente
| status                 = [[Military alliance]]
| year_start             = 1914
| year_end               = 1918|membership = {{ubli
 | {{flag|French Third Republic|name=French Republic}}
 | {{flag|British Empire}}
   | &nbsp;•&nbsp;{{flagcountry|United Kingdom of Great Britain and Ireland}}
   | &nbsp;•&nbsp;{{flag|Canada|1907}}
   | &nbsp;•&nbsp;{{flag|Australia}}
   | &nbsp;•&nbsp;{{flagcountry|Union of South Africa|1912}}
   | &nbsp;•&nbsp;{{flagcountry|Dominion of New Zealand}}
   | &nbsp;•&nbsp;{{flagcountry|British Raj|Viceroy}}
 | {{flag|Kingdom of Italy}} (from 1915)
 | {{flag|Russian Empire}} (until 1917)
 | {{flag|United States|1912}} (from 1917)
 | {{flag|Empire of Japan}}
}}''...see {{slink||Affiliated state combatants}}''
| image_map              = File:World War I alliances.png
| map_caption            = Allies in blue; [[Central Powers]] in orange
| era                    = World War I
}}
[[File:I0032385.tif|thumb|British recruitment poster, 1915, incorporating the [[Union Jack]], the [[French flag|French]] and [[Belgian flag|Belgian]] flags, and the [[Ensign of the Russian Navy]].]]
The '''Allies''' or the '''Entente''' ({{IPAc-en|UK|ɒ̃|ˈ|t|ɒ̃|t}}, {{IPAc-en|US|ɒ|n|ˈ|t|ɒ|n|t}} {{respell|on|TONT}}) was an international military [[coalition]] of countries led by the [[French Third Republic|French Republic]], the [[United Kingdom of Great Britain and Ireland|United Kingdom]], the [[Russian Empire]], the [[United States]], the [[Kingdom of Italy]], and the [[Empire of Japan]] against the [[Central Powers]] of the [[German Empire]], [[Austria-Hungary]], the [[Ottoman Empire]], and the [[Kingdom of Bulgaria]] in [[World War I]] (1914–1918).

By the end of the first decade of the 20th century, the major European powers were divided between the [[Triple Entente]] and the [[Triple Alliance (1882)|Triple Alliance]]. The Triple Entente was made up of the United Kingdom, France, and Russia. The Triple Alliance was originally composed of Germany, Austria–Hungary, and Italy, but Italy remained neutral in 1914. As the war progressed, each coalition added new members. Japan joined the Entente in 1914 and, despite proclaiming its neutrality at the beginning of the war, Italy also joined the Entente in 1915. The term "Allies" became more widely used than "Entente",{{Citation needed|date=January 2024}} although the United Kingdom, France, Russia, and Italy were also referred to as the '''Quadruple Entente''' and, together with Japan, as the '''Quintuple Entente'''.<ref>{{cite book | url=https://books.google.com/books?id=P2DNDwAAQBAJ&dq=quadruple+entente&pg=PA63 | title=History of International Relations and Russian Foreign Policy in the 20th Century (Volume I) | isbn=9781527545021 | last1=Torkunov | first1=Anatoly V. | last2=Martyn | first2=Boris F. | last3=Wohlforth | first3=William C. | date=8 January 2020 | publisher=Cambridge Scholars }}</ref><ref>{{Cite book|url=https://books.google.com/books?id=P2DNDwAAQBAJ&q=quintuple+entente&pg=PA62|title = History of International Relations and Russian Foreign Policy in the 20th Century (Volume I)|isbn = 978-1-5275-4502-1|last1 = Torkunov|first1 = Anatoly V.|last2 = Wohlforth|first2 = William C.|last3 = Martyn|first3 = Boris F.|date = 8 January 2020| publisher=Cambridge Scholars }}</ref> The five [[British Dominions]] ([[Australia]], [[Canada]], [[New Zealand]], [[Newfoundland]], and the [[Union of South Africa]]) all fought alongside the British.  The colonies of Allied countries, such as the [[Insular Government of the Philippine Islands|American Philippines]], [[Belgian Congo]], [[British Raj|British India]], [[French Algeria]], and [[Korea under Japanese rule|Japanese Korea]], were also used as a source of manpower by the colonial powers.

The United States joined near the end of the war in 1917 (the same year in which Russia withdrew from the conflict) as an "associated power" rather than an official ally. Primary reasons for why the United States joined the war include the unrestricted submarine warfare waged by Germany in the Atlantic, the revelation of the [[Zimmermann telegram]], and strong economic and political ties with the Allies. Other "associated members" of the Allies included [[Kingdom of Serbia|Serbia]], [[Belgium]], [[Kingdom of Montenegro|Montenegro]], [[Idrisid Emirate of Asir|Asir]], [[Emirate of Nejd and Hasa|Nejd and Hasa]], [[First Portuguese Republic|Portugal]], [[Kingdom of Romania|Romania]], [[Kingdom of Hejaz|Hejaz]], [[Panama]], [[Republic of Cuba (1902–1959)|Cuba]], [[Kingdom of Greece|Greece]], [[Beiyang government|China]], [[Rattanakosin Kingdom (1782–1932)|Siam]], [[First Brazilian Republic|Brazil]], [[First Republic of Armenia|Armenia]], [[Luxembourg]], [[Guatemala]], [[Nicaragua]], [[First Costa Rican Republic|Costa Rica]], [[Republic of Haiti (1859–1957)|Haiti]], [[Liberia]], and [[Honduras]].<ref>Karel Schelle, ''The First World War and the Paris Peace Agreement'', GRIN Verlag, 2009, [https://books.google.com/books?id=4lsOsKQz3AQC&pg=PA24 p. 24]</ref> The treaties signed at the [[Paris Peace Conference (1919–1920)|Paris Peace Conference]] recognized the British Empire, France, Italy, Japan, and the United States as "the Principal Allied and Associated Powers";<ref>Preamble, [http://www.austlii.edu.au/au/other/dfat/treaties/1920/1.html Treaty of Versailles] Australian Treaty Series 1920 No 1</ref> France, the UK, Italy, and the US were also referred as the "[[Big Four (World War I)|Big Four]]" top powers of the war.<ref>{{cite web|url=http://www.history.com/this-day-in-history/leaders-of-the-big-four-nations-meet-for-the-first-time-in-paris|title=Leaders of the Big Four nations meet for the first time in Paris|work=history.com|date=16 November 2009 }}</ref>

==Background==
When the war began in 1914, the [[Central Powers]] were opposed by the [[Triple Entente]], formed in 1907 when the agreement between the United Kingdom and [[Russian Empire|Russia]] complemented existing agreements between the three powers.

Fighting commenced when Austria invaded [[Kingdom of Serbia|Serbia]] on 28 July 1914, in response to the [[assassination of Archduke Franz Ferdinand]], heir to Emperor [[Franz Joseph I of Austria|Franz Joseph I]]; this brought Serbia's ally [[Kingdom of Montenegro|Montenegro]] into the war on 9 August and it attacked the Austrian naval base at [[Kotor|Cattaro]], modern Kotor.{{sfn|Gilbert|1995|p=44}} At the same time, German troops carried out the [[Schlieffen Plan]], entering neutral [[Belgium]] and [[Luxembourg]]; over 95% of Belgium was occupied but the Belgian Army held their lines on the [[Yser Front]] throughout the war. This allowed Belgium to be treated as an Ally, in contrast to Luxembourg which retained control over domestic affairs but was [[German occupation of Luxembourg during World War I|occupied by the German military]].

In the East, between 7 and 9 August the Russians entered German [[Russian invasion of East Prussia (1914)|East Prussia]] and Austrian [[Russian occupation of Eastern Galicia, 1914–15|Eastern Galicia]]. [[Empire of Japan|Japan]] joined the Entente by declaring war on Germany on 23 August, then Austria on 25 August.<ref>Mizokami, Kyle, "[http://www.japantimes.co.jp/news/2014/07/26/national/history/japans-baptism-of-fire/ Japan's baptism of fire: World War I put country on a collision course with West] {{Webarchive|url=https://web.archive.org/web/20180731062152/https://www.japantimes.co.jp/news/2014/07/26/national/history/japans-baptism-of-fire/ |date=31 July 2018 }}", ''[[The Japan Times]]'', 27 July 2014</ref> On 2 September, Japanese forces surrounded the German [[Treaty ports|Treaty Port]] of [[Qingdao|Tsingtao]] (now Qingdao) in China and occupied German colonies in the Pacific, including the [[Mariana Islands|Mariana]], [[Caroline Islands|Caroline]], and [[Marshall Islands]].

Despite its membership of the [[Triple Alliance (1882)|Triple Alliance]], [[Kingdom of Italy|Italy]] remained neutral until 23 May 1915 when it joined the Entente, declaring war on Austria but not Germany. On 17 January 1916, [[Kingdom of Montenegro|Montenegro]] capitulated and left the Entente;{{sfn|Gilbert|1995|p=225}} this was offset when Germany declared war on [[First Portuguese Republic|Portugal]] in March 1916, while [[Kingdom of Romania|Romania]] commenced hostilities against Austria on 27 August.{{sfn|Gilbert|1995|p=282}}

On 6 April 1917, the United States entered the war as a co-belligerent, along with the associated allies of [[Liberia]], [[Rattanakosin Kingdom|Siam]] and [[Kingdom of Greece|Greece]]. After the 1917 [[October Revolution]], Russia left the Entente and agreed to a separate peace with the Central Powers with the signing of the [[Treaty of Brest-Litovsk]] on 3 March 1918. Romania was forced to do the same in the May 1918 [[Treaty of Bucharest (1918)|Treaty of Bucharest]] but on 10 November, it repudiated the Treaty and once more declared war on the Central Powers.

These changes meant the Allies who negotiated the [[Treaty of Versailles]] in 1919 included the United Kingdom, France, Italy, Japan and the United States; Part One of the Treaty agreed to the establishment of the [[League of Nations]] on 25 January 1919.<ref>{{cite book |last1=Magliveras |first1=Konstantin |title=Exclusion from Participation in International Organisations: The Law and Practice Behind Member States' Expulsion and Suspension of Membership |date=1999 |publisher=Brill |isbn=978-90-411-1239-2 |pages=8–12}}</ref> This came into being on 16 January 1920 with Britain, France, Italy and Japan as permanent members of the Executive Council; the [[United States Senate|US Senate]] voted against ratification of the treaty on 19 March, thus preventing the United States from joining the League.

{{Clear}}

==Statistics==
For similar statistics of the Central Powers, see [[Central Powers#Statistics]].

{| class="wikitable plainrowheaders" style="text-align: right;"
|+Statistics of the Allied Powers (1913) and enlisted soldiers during the war<ref>{{cite book|url=https://books.google.com/books?id=rpBbX3kdnhgC&pg=PA7|author1=S.N. Broadberry|author2=Mark Harrison|title=The Economics of World War I. illustrated|publisher=Cambridge University Press|year=2005|page=7|access-date=2015-03-16|isbn=978-1-139-44835-2}}</ref> <!-- Don't change any numbers until you cite a reliable source and/or have discussed on talk page with other users. -->
! scope="col" colspan=2 | Country
! scope="col" | Population {{wrap|(millions)}}
! scope="col" | Land {{nowrap|(million km<sup>2</sup>)}}
! scope="col" | GDP {{nowrap|($ billion, 1990 prices)}}
! scope="col" | Mobilized personnel
|-
! scope="col" colspan=6 | First Wave (1914)
|-
! scope="row" rowspan=3 | [[Russian Empire]]
! scope="row" | Russia 
(inc. [[Congress Poland]] and 
[[Vistula Land]])
| 173.2
| 21.7
| 257.7
| rowspan="3" | 12,000,000<ref name =Tucker172/>
|-
! scope="row" | [[Grand Duchy of Finland|Finland]]
| 3.2
| 0.4
| 6.6
|-
! scope="row" style="font-weight: bold;" | Total
| 176.4
| 22.1
| 264.3
|-
! scope="row" rowspan=3 | [[French Third Republic|French Republic]]
! scope="row" | France
| 39.8
| 0.5
| 138.7
| rowspan="3" | 8,410,000<ref name=Tucker172>{{cite book |last=Tucker |first=Spencer C |title=The European Powers in the First World War: An Encyclopedia |publisher=Garland |place=New York |year=1999 |isbn=978-0-8153-3351-7 |page=172}}</ref>
|-
! scope="row" | [[French colonial empire#Evolution in the use of the term Empire between the years of 1870–1939|French colonies]]
| 48.3
| 10.7
| 31.5
|-
! scope="row" style="font-weight: bold;" | Total
| 88.1
| 11.2
| 170.2
|-
! scope="row" rowspan=4 | [[British Empire#First World War|British Empire]]
! scope="row" | [[United Kingdom of Great Britain and Ireland|United Kingdom]]
| 46.0
| 0.3
| 226.4
| 6,211,922<ref name=Gilbert94>{{cite book |last=Gilbert |first=Martin |title=Atlas of World War I |publisher=Oxford University Press |year=1994 |isbn=978-0-19-521077-4 |oclc=233987354 }}</ref>
|-
! scope="row" | [[Crown colony|British colonies]]
| 380.2
| 13.5
| 257
| 1,440,437{{sfn|War Office Statistics|2006|p=756}}<ref>[[Indian Army during World War I|Indian Army]] only</ref>
|-
! scope="row" | British [[Dominion]]s
| 19.9
| 19.5
| 77.8
| 1,307,000{{sfn|War Office Statistics|2006|p=756}}
|-
! scope="row" style="font-weight: bold;" | Total
| 446.1
| 33.3
| 561.2
| 8,689,000<ref>{{cite web|url=http://www.1914-1918.net/faq.htm|title=Some British Army statistics of the Great War|last=Baker|first=Chris|website=1914-1918.net|language=en|access-date=2017-08-07|archive-url=https://web.archive.org/web/20170718163308/http://www.1914-1918.net/faq.htm|archive-date=2017-07-18}}</ref>
|-
! scope="row" rowspan=3 | [[Empire of Japan]]
! scope="row" | Japan
| 55.1
| 0.4
| 76.5
| rowspan="3" | 800,000<ref name =Tucker172/>
|-
! scope="row" | [[Japanese colonial empire|Japanese colonies]]<ref>[[Korea under Japanese rule|Korea]], [[Taiwan under Japanese rule|Formosa]], [[Kwantung Leased Territory|Kwantung]] and [[Karafuto Prefecture|Sakhalin]]</ref>
| 19.1
| 0.3
| 16.3
|-
! scope="row" style="font-weight: bold;" | Total
| 74.2
| 0.7
| 92.8
|-
! scope="row" colspan=2 | [[Kingdom of Serbia|Serbia]], [[Kingdom of Montenegro|Montenegro]], and [[Austro-Hungarian rule in Bosnia and Herzegovina|Bosnia and Herzegovina]]
| 7.0
| 0.2
| 7.2
| 760,000<ref name =Tucker172/>
|-
! scope="col" colspan=6 | Second Wave (1915–1916)
|-
! scope="row" rowspan=3 | [[Kingdom of Italy]]
! scope="row" | Italy
| 35.6
| 0.3
| 91.3
| rowspan="3" | 5,615,000<ref name =Tucker172/>
|-
! scope="row" | [[Italian Empire#World War I and aftermath|Italian colonies]]
| 2.0
| 2.0
| 1.3
|-
! scope="row" style="font-weight: bold;" | Total
| 37.6
| 2.3
| 92.6
|-
! scope="row" rowspan=3 | [[First Portuguese Republic|Portuguese Republic]]
! scope="row" | Portugal
| 6.0
| 0.1
| 7.4
| rowspan="3" | 100,000<ref name =Tucker172/>
|-
! scope="row" | [[Portuguese Empire#World War I|Portuguese colonies]]
| 8.7
| 2.4
| 5.2
|-
! scope="row" style="font-weight: bold;" | Total
| 14.7
| 2.5
| 12.6
|-
! scope="row" colspan=2 | [[Kingdom of Romania]]
| 7.7
| 0.1
| 11.7
| 750,000<ref name =Tucker172/>
|-
! scope="col" colspan=6 | Third Wave (1917–1918)
|-
! scope="row" rowspan=3 | [[United States]] of America
! scope="row" | United States
| 96.5
| 7.8
| 511.6
| rowspan="3" | 4,355,000<ref name=Tucker172/>
|-
! scope="row" | [[United States territorial acquisitions#Since 1853|overseas dependencies]]<ref>As [[Territory of Hawaii|Hawaii]] and [[Territory of Alaska|Alaska]] were not yet [[U.S. state]]s, they are included in the dependencies.</ref>
| 9.8
| 1.8
| 10.6
|-
! scope="row" style="font-weight: bold;" | Total
| 106.3
| 9.6
| 522.2
|-
! scope="row" colspan=2 | [[Central America]]n states<ref>Costa Rica, Cuba, Guatemala, Haiti, Honduras, Nicaragua and Panama</ref>
| 9.0
| 0.6
| 10.6
|
|-
! scope="row" colspan=2 | [[First Brazilian Republic|Republic of the United States of Brazil]]
| 25.0
| 8.5
| 20.3
| 1,713<ref>{{cite book |author=Hernâni Donato |title=Dicionário das Batalhas Brasileiras |year=1987 |location=Rio de Janeiro |publisher=IBRASA |isbn=978-85-348-0034-1}}</ref>
|-
! scope="row" colspan=2 | [[Kingdom of Greece]]
| 4.8
| 0.1
| 7.7
| 230,000<ref name =Tucker172/>
|-
! scope="row" colspan=2 | [[Rattanakosin Kingdom (1782–1932)|Kingdom of Siam]]
| 8.4
| 0.5
| 7.0
| 1,284<ref name=Gilbert94/>
|-
! scope="row" colspan=2 | [[Republic of China (1912–1949)|Republic of China]]
| 441.0
| 11.1
| 243.7
|
|-
! scope="row" colspan=2 | [[Liberia|Republic of Liberia]]
| 1.5
| 0.1
| 0.9
|
|}

{| class="wikitable plainrowheaders" style="text-align: right;"
|+ Aggregate statistics of the Allied Powers (in 1913)<ref>{{cite book|url=https://books.google.com/books?id=rpBbX3kdnhgC&pg=PA8|author1=S.N. Broadberry|author2=Mark Harrison|title=The Economics of World War I. illustrated|publisher=Cambridge University Press|year=2005|page=8|access-date=2015-03-16|isbn=978-1-139-44835-2}}</ref> <!-- Don't change any numbers until you cite a reliable source and/or have discussed on talk page with other users. -->
|-
! scope="col" | Group
! scope="col" | Population {{nowrap|(millions)}}
! scope="col" | Territory {{nowrap|(million km<sup>2</sup>)}}
! scope="col" | GDP {{nowrap|($ billion)}}
|-
! scope="col" colspan=6 | November 1914
|-
! scope="row" | Allies, total
| 793.3
| 67.5
| 1,096.5
|-
! scope="row" | UK, France and Russia only
| 259.0
| 22.6
| 622.8
|-
! scope="col" colspan=6 | November 1916
|-
! scope="row" | Allies, total
| 853.3
| 72.5
| 1,213.4
|-
! scope="row" | UK, France and Russia only<!-- this row seems off: identical to November 1914 numbers -->
| 259.0
| 22.6
| 622.8
|-
! scope="col" colspan=6 | November 1918
|-
! scope="row" | Allies, total
| 1,271.7
| 80.8
| 1,760.5
|-
! scope="row" | Percentage of world
| 70%
| 61%
| 64%
|-
! scope="row" | UK, France and US only
| 182.3
| 8.7
| 876.6
|-
! scope="row" | Percentage of world
| 10%
| 7%
| 32%
|- class="sortbottom" style="text-align: right;"
! scope="row" style="font-weight: bold;" | [[Central Powers#Statistics|Central Powers]]<ref>Germany (and colonies), Austria-Hungary, Ottoman Empire and Bulgaria</ref>
! style="text-align: right;" | 156.1
! style="text-align: right;" | 6.0
! style="text-align: right;" | 383.9
|- class="sortbottom" style="text-align: right;"
! scope="row" style="font-weight: bold;" | World, 1913
! style="text-align: right;" | 1,810.3
! style="text-align: right;" | 133.5
! style="text-align: right;" | 2,733.9
|}

==Principal powers==
===British Empire===
{{Main|British entry into World War I|History of the United Kingdom during the First World War|Splendid isolation}}
[[File:British Empire in 1914.png|thumb|left|350px|The British Empire in 1914]]
For much of the 19th century, Britain sought to maintain the European balance of power without formal alliances, a policy known as [[splendid isolation]]. This left it dangerously exposed as Europe divided into opposing power blocs.  In response, the [[Unionist government, 1895–1905|1895–1905 Conservative government]] negotiated first the 1902 [[Anglo-Japanese Alliance]], then the 1904 [[Entente Cordiale]] with France.<ref>Avner Cohen, "Joseph Chamberlain, Lord Lansdowne and British foreign policy 1901–1903: From collaboration to confrontation", ''Australian Journal of Politics & History'' 43#2 (1997): 122–134.</ref> The first tangible result of this shift was British support for France against Germany in the [[First Moroccan Crisis|1905 Moroccan Crisis]].

The [[Liberal government, 1905–1915|1905–1915 Liberal government]] continued this re-alignment with the 1907 [[Anglo-Russian Convention]]. Like the Anglo-Japanese and Entente agreements, it focused on settling colonial disputes but by doing so paved the way for wider co-operation and allowed Britain to refocus resources in response to [[Anglo-German naval arms race|German naval expansion]].<ref>{{cite book |last1=Massie |first1=Robert |title=Dreadnought: Britain, Germany and the Coming of the Great War |date=2007 |publisher=Vintage |isbn=978-0-09-952402-1 |pages=466–468 |edition=2013}}</ref>
[[File:HMS Dreadnought 1906 H61017.jpg|thumb|250px|[[HMS Dreadnought (1906)|HMS ''Dreadnought'']]; the 1902, 1904 and 1907 agreements with Japan, France and Russia allowed Britain to refocus resources during the [[Anglo-German naval arms race]].]]

Since control of Belgium allowed an opponent to threaten invasion or blockade British trade, preventing it was a long-standing British strategic interest.{{efn|The consequences were demonstrated when Germany controlled these areas during 1940–1944.}}<ref>{{cite journal |last1=Nilesh |first1=Preeta |title=Belgian Neutrality and the First world War; Some Insights |journal=Proceedings of the Indian History Congress |date=2014 |volume=75 |page=1014 |jstor=44158486 }}</ref> Under Article VII of the 1839 [[Treaty of London (1839)|Treaty of London]], Britain guaranteed Belgian neutrality against aggression by any other state, by force if required.<ref>{{cite book |last1=Hull |first1=Isabel |title=A Scrap of Paper: Breaking and Making International Law during the Great War |date=2014 |publisher=Cornell University Press |isbn=978-0-8014-5273-4 |page=17}}</ref> Chancellor [[Theobald von Bethmann Hollweg]] later dismissed this as a 'scrap of paper,' but British law officers routinely confirmed it as a binding legal obligation and its importance was well understood by Germany.<ref>{{cite journal |last1=Schreuder |first1=Deryck |title=Gladstone as "Troublemaker": Liberal Foreign Policy and the German Annexation of Alsace-Lorraine, 1870–1871 |journal=Journal of British Studies |date=Spring 1978 |volume=17 |issue=2 |pages=108–109 |doi=10.1086/385724 |jstor=175393 |s2cid=145137541 }}</ref>

The 1911 [[Agadir Crisis]] led to secret discussions between France and Britain in case of war with Germany. These agreed that within two weeks of its outbreak, a [[British Expeditionary Force (World War I)|British Expeditionary Force]] of 100,000 men would be landed in France; in addition, the [[Royal Navy]] would be responsible for the [[North Sea]], the [[English Channel|Channel]] and protecting Northern France, with the French navy concentrated in the [[Mediterranean Sea|Mediterranean]].<ref>{{cite book |last1=Jenkins |first1=Roy |title=Asquith |date=1964 |publisher=Harpers Collins |isbn=978-0-00-217358-2 |pages=242–245 |edition=1988 Revised and Updated}}</ref> Britain was committed to support France in a war against Germany but this was not widely understood outside government or the upper ranks of the military.

As late as 1 August, a clear majority of the Liberal government and its supporters wanted to stay out of the war.<ref>{{cite book|author=Catriona Pennell|title=A Kingdom United: Popular Responses to the Outbreak of the First World War in Britain and Ireland|url=https://books.google.com/books?id=lVK0SSmvD5wC&pg=PA27|year=2012|page=27|publisher=OUP Oxford |isbn=978-0-19-959058-2}}</ref> While Liberal leaders [[H. H. Asquith]] and [[Edward Grey, 1st Viscount Grey of Fallodon|Edward Grey]] considered Britain legally and morally committed to support France regardless, waiting until Germany triggered the 1839 Treaty provided the best chance of preserving Liberal party unity.<ref>{{cite book |last1=Cassar |first1=George |title=Asquith as War Leader |date=1994 |publisher=Bloomsbury |isbn=978-1-85285-117-0 |pages=14–17}}</ref>
[[File:New Names Canadian WW1 recruiting poster.jpg|thumb|left|200px|Canadian Army recruitment poster]]
The German high command was aware entering Belgium would lead to British intervention but decided the risk was acceptable; they expected a short war while their ambassador in London claimed troubles in Ireland would prevent Britain from assisting France.<ref name="auto">{{cite book |editor1=Brock, Michael |editor2=Brock, Elinor |title=Margot Asquith's Great War Diary 1914–1916: The View from Downing Street |date=2014 |publisher=OUP Oxford; Reprint edition |pages=852–864 |isbn=978-0-19-873772-8 |edition=Kindle }}</ref> On 3 August, Germany demanded unimpeded progress through any part of Belgium and when this was refused, invaded early on the morning of 4 August.

This changed the situation; the invasion of Belgium consolidated political and public support for the war by presenting what appeared to be a simple moral and strategic choice.<ref>{{cite journal |last1=Gullace |first1=Nicoletta F |title=Sexual Violence and Family Honor: British Propaganda and International Law during the First World War |journal=The American Historical Review |date=June 1997 |volume=102 |issue=3 |page=717 |doi=10.2307/2171507 |jstor=2171507 }}</ref> The Belgians asked for assistance under the 1839 Treaty and in response, Britain declared war on Germany on 4 August 1914.<ref>Tucker, Spencer C. A Global Chronology of Conflict: From the Ancient World to the Modern Middle East: From the Ancient World to the Modern Middle East. ABC-CLIO. 2009. P1562.</ref> Although Germany's violation of Belgium neutrality was not the only cause of British entry into the war, it was used extensively in government propaganda at home and abroad to make the case for British intervention.<ref>{{cite book|author=Stephen J. Lee|title=Aspects of British Political History 1914–1995|url=https://books.google.com/books?id=LKGFAgAAQBAJ&pg=PA21|year=2005|pages=21–22|publisher=Routledge |isbn=978-1-134-79040-1}}</ref> This confusion arguably persists today.

The declaration of war automatically involved all [[Dominion]]s, colonies, and protectorates of the [[British Empire]], many of whom made significant contributions to the Allied war effort, both in the provision of troops and civilian labourers. It was split into [[Crown Colonies]] administered by the [[Colonial Office]] in London, such as [[Colony and Protectorate of Nigeria|Nigeria]],{{Efn|Others included [[Gibraltar]], [[Cyprus]], [[Malta]], [[East Africa Protectorate]], [[Nyasaland]], [[Northern Rhodesia|Northern]] and [[Southern Rhodesia]], the [[Uganda Protectorate]], the [[Gold Coast (British colony)|Gold Coast]], [[Colony and Protectorate of Nigeria|Nigeria]], [[British Honduras]], the [[Falkland Islands]], [[British Guiana]], the [[British West Indies]], [[British Malaya]], [[North Borneo]], [[British Ceylon|Ceylon]] and [[British Hong Kong|Hong Kong]].}} and the self-governing Dominions of [[Australia]], [[Canada]], [[Dominion of New Zealand|New Zealand]], [[Dominion of Newfoundland|Newfoundland]], and [[Union of South Africa|South Africa]]. These controlled their own domestic policies and military expenditure but not foreign policy.
[[File:IndianArmyMGCrewFlanders1914-15(1).jpg|thumb|220px|Indian soldiers of the [[2nd Queen Victoria's Own Rajput Light Infantry|2nd Rajput Light Infantry]] on the [[Western Front (World War I)|Western Front]], winter of 1914–15]]

In terms of population, the largest component (after Britain herself) was the [[British Raj]] or British India, which included modern [[India]], [[Pakistan]], [[Myanmar]] and [[Bangladesh]]. Unlike other colonies which came under the [[Colonial Office]], it was governed directly by the [[India Office]] or by [[Princely state|princes loyal]] to the British; it also controlled British interests in the [[Persian Gulf]], such as the [[Trucial States]] and [[Oman]]. Over one million soldiers of the [[British Indian Army]] served in different theatres of the war, primarily France and the [[Middle Eastern theatre of World War I|Middle East]].

From 1914 to 1916, overall Imperial diplomatic, political and military strategy was controlled by the [[War Cabinet#First World War|British War Cabinet]] in London; in 1917 it was superseded by the [[Imperial War Cabinet]], which included representatives from the Dominions.<ref>{{cite journal |last1=Schuyler |first1=Robert Livingston |title=The British Cabinet, 1916–1919 |journal=Political Science Quarterly |date=March 1920 |volume=35 |issue=1 |pages=77–93 |doi=10.2307/2141500 |jstor=2141500 }}</ref> Under the War Cabinet were the [[Chief of the General Staff (United Kingdom)|Chief of the Imperial General Staff or CIGS]], responsible for all Imperial ground forces, and the [[Admiralty (United Kingdom)|Admiralty]] that did the same for the [[Royal Navy]]. Theatre commanders like [[Douglas Haig, 1st Earl Haig|Douglas Haig]] on the [[Western Front (World War I)|Western Front]] or [[Edmund Allenby, 1st Viscount Allenby|Edmund Allenby]] in [[Sinai and Palestine Campaign|Palestine]] then reported to the CIGS.

After the Indian Army, the largest individual units were the [[Australian Corps]] and [[Canadian Corps]] in France, which by 1918 were commanded by their own generals, [[John Monash]] and [[Arthur Currie]].<ref>Perry (2004), p.xiii</ref> Contingents from South Africa, New Zealand and Newfoundland served in theatres including France, [[Gallipoli Campaign|Gallipoli]], [[German East Africa]] and the Middle East. Australian troops separately occupied [[German New Guinea]], with the South Africans doing the same in [[German South West Africa]]; this resulted in the [[Maritz rebellion]] by former Boers, which was quickly suppressed. After the war, New Guinea and South-West Africa became [[Protectorate]]s, held until 1975 and 1990 respectively.

===Russia===
{{Main|Russian entry into World War I|Russian Empire}}
[[File:Russian Troops NGM-v31-p372.jpg|thumb|250px|left|Russian troops marching to the front]]
Between 1873 and 1887, Russia was allied with Germany and Austria-Hungary in the [[League of the Three Emperors]], then with Germany in the 1887–1890 [[Reinsurance Treaty]]; both collapsed due to the competing interests of Austria and Russia in the [[Balkans]]. While France took advantage of this to agree the 1894 [[Franco-Russian Alliance]], Britain viewed Russia with deep suspicion; in 1800, over 3,000 kilometres separated the Russian Empire and British India, by 1902, it was 30&nbsp;km in some areas.<ref>{{cite book |last1=Hopkirk |first1=Peter |title=The Great Game; On Secret Service in High Asia |date=1990 |publisher=OUP |isbn=978-0-7195-6447-5 |pages=4–5 |edition=1991}}</ref> This threatened to bring the two into direct conflict, as did the long-held Russian objective of gaining control of the [[Bosporus|Bosporus Straits]] and with it access to the British-dominated [[Mediterranean Sea]].<ref name="The Freedom of the Straits">{{cite journal |last1=Dennis |first1=Alfred L.P. |title=The Freedom of the Straits |journal=The North American Review |date=December 1922 |volume=216 |issue=805 |pages=728–729 |jstor=25112888 }}</ref>
[[File:Russian poster WWI 083.jpg|thumb|200px|Russian recruiting poster; the caption reads 'World on fire; Second Patriotic War'.]]
Russian defeat in the 1905 Russo-Japanese War and Britain's isolation during the 1899–1902 [[Second Boer War]] led both parties to seek allies. The [[Anglo-Russian Convention]] of 1907 settled disputes in Asia and allowed the establishment of the Triple Entente with France, which at this stage was largely informal. In 1908, Austria annexed the former Ottoman province of [[Bosnia and Herzegovina]]; Russia responded by creating the [[Balkan League]] in order to prevent further Austrian expansion.<ref name=":0">{{cite book |last1=Stowell |first1=Ellery Cory |title=The Diplomacy of the War of 1914: The Beginnings of the War |date=1915 |publisher=Kessinger Publishing |isbn=978-1-165-81956-0 |page=94 |edition=2010}}</ref> In the 1912–1913 [[First Balkan War]], [[Kingdom of Serbia|Serbia]], [[Kingdom of Bulgaria|Bulgaria]] and [[Kingdom of Greece|Greece]] captured most of the remaining Ottoman possessions in Europe; disputes over the division of these resulted in the [[Second Balkan War]], in which Bulgaria was comprehensively defeated by its former allies.

Russia's industrial base and railway network had significantly improved since 1905, although from a relatively low base; in 1913, [[Nicholas II of Russia|Tsar Nicholas]] approved an increase in the Russian Army of over 500,000 men. Although there was no formal alliance between Russia and Serbia, their close bilateral links provided Russia with a route into the crumbling Ottoman Empire, where Germany also had significant interests. Combined with the increase in Russian military strength, both Austria and Germany felt threatened by Serbian expansion; when Austria invaded Serbia on 28 July 1914, Russian Foreign Minister [[Sergey Sazonov]] viewed it as an Austro-German conspiracy to end Russian influence in the Balkans.<ref>{{cite book |last1=Jelavich |first1=Barbara |title=Russia's Balkan Entanglements |date=2008 |publisher=Cambridge University Press |isbn=978-0-521-52250-2 |page=262}}</ref>

In addition to its own territory, Russia viewed itself as the defender of its fellow [[Pan-Slavism|Slavs]] and on 30 July, mobilized in support of Serbia. In response, Germany declared war on Russia on 1 August, followed by Austria-Hungary on 6th; after Ottoman warships bombarded [[Odessa]] in late October, the Entente declared war on the Ottoman Empire in November 1914.<ref>{{cite book |editor1=Afflerbach, Holger |editor2=Stevenson, David |author=Aksakal, Mustafa |chapter=War as a Saviour? Hopes for War & Peace in Ottoman Politics before 1914 |title=An Improbable War? the Outbreak of World War I and European Political Culture Before 1914 |date=2012 |publisher=Berghahn Books |isbn=978-0-85745-310-5 |page=293}}</ref>

===France===
{{Main|French entry into World War I|French Third Republic}}
[[File:Georges Scott, A la baïonnette !.jpg|thumb|200px|French bayonet charge, 1914]]
French defeat in the 1870–1871 [[Franco-Prussian War]] led to the loss of the two provinces of [[Alsace-Lorraine]] and the establishment of the [[French Third Republic|Third Republic]]. The suppression of the [[Paris Commune]] by the new regime caused deep political divisions and led to a series of bitter political struggles, such as the [[Dreyfus affair]]. As a result, aggressive nationalism or [[Revanchism]] was one of the few areas to unite the French.

The loss of Alsace-Lorraine deprived France of its natural defence line on the [[Rhine]], while it was weaker demographically than Germany, whose 1911 population was 64.9&nbsp;million to 39.6 in France, which had the lowest birthrate in Europe.<ref>{{cite web |last1=Baux |first1=Jean-Pierre |title=1914; A Demographically Weakened France |url=http://www.cheminsdememoire.gouv.fr/en/1914-demographically-weakened-france |website=Chemins de Memoire |access-date=18 August 2018 |archive-url=https://web.archive.org/web/20180819120630/http://www.cheminsdememoire.gouv.fr/en/1914-demographically-weakened-france |archive-date=19 August 2018 |url-status=live }}</ref> This meant that despite their very different political systems, when Germany allowed the Reinsurance Treaty to lapse, France seized the opportunity to agree the 1894 [[Franco-Russian Alliance]]. It also replaced Germany as the primary source of financing for Russian industry and the expansion of its railway network, particularly in border areas with Germany and Austria-Hungary.<ref>{{cite book |last1=Starns |first1=Karl M |title=The Russian Railways and Imperial Intersections in the Russian Empire |date=2012 |publisher=Master of Arts in International Studies Thesis for Washington University |pages=47–49 |url=https://digital.lib.washington.edu/researchworks/bitstream/handle/1773/21998/Starns_washington_0250O_10676.pdf |access-date=19 August 2018 |archive-url=https://web.archive.org/web/20170326050558/https://digital.lib.washington.edu/researchworks/bitstream/handle/1773/21998/Starns_washington_0250O_10676.pdf |archive-date=26 March 2017 |url-status=live }}</ref>
[[File:French Colonial Forces.jpg|thumb|left|200px|French [[Zouave]]s of the [[Army of Africa (France)|Army of Africa]]]]
However, Russian defeat in the 1904–1905 [[Russo-Japanese War]] damaged its credibility, while Britain's isolation during the [[Second Boer War]] meant both countries sought additional allies. This resulted in the 1904 [[Entente Cordiale]] with Britain; like the 1907 [[Anglo-Russian Convention]], for domestic British consumption it focused on settling colonial disputes but led to informal co-operation in other areas. By 1914, both the British army and [[Royal Navy]] were committed to support France in the event of war with Germany but even in the British government, very few were aware of the extent of these commitments.<ref name=":1">{{cite book |editor1=Brock, Michael |editor2=Brock, Elinor |title=Margot Asquith's Great War Diary 1914–1916: The View from Downing Street |date=2014 |publisher=OUP Oxford; Reprint edition |pages=759–781 |isbn=978-0-19-873772-8 |edition=Kindle }}</ref>
[[File:French 75 gun at Cape Helles 1915.jpg|thumb|200px|French artillery in action near [[Gallipoli campaign|Gallipoli]], 1915]]
In response to Germany's declaration of war on Russia, France issued a general mobilisation in expectation of war on 2 August and on 3 August, Germany also declared war on France.<ref>Tucker, Spencer C. ''A Global Chronology of Conflict: From the Ancient World to the Modern Middle East: From the Ancient World to the Modern Middle East''. ABC-CLIO. 2009. p. 1556.</ref> Germany's ultimatum to Belgium brought Britain into the war on 4 August, although France did not declare war on Austria-Hungary until 12 August.

As with Britain, France's [[French colonial empire|colonies]] also became part of the war; pre-1914, French soldiers and politicians advocated using French African recruits to help compensate for France's demographic weakness. But it eventually proved useless, the soldiers from [[Metropolitan France]] still undertook all the tasks.<ref>{{cite journal |last1=Hargreaves |first1=John |title=French West Africa in the First World War; a review of L'Appel à l'Afrique. Contributions et Réactions à l'Effort de guerre en A.O.F. (1914–1919) by Marc Michel |journal=The Journal of African History |date=1983 |volume=24 |issue=2 |pages=285–288 |jstor=181646 |doi=10.1017/S002185370002199X |s2cid=161424205 }}</ref> From August to December 1914, the French lost nearly 300,000 dead on the Western Front, more than Britain suffered in the whole of WWII and the gaps were partly filled by colonial troops, over 500,000 of whom served on the Western Front over the period 1914–1918.<ref>{{cite web |last1=Koller |first1=Christian |title=Colonial Military Participation in Europe |url=https://encyclopedia.1914-1918-online.net/article/colonial_military_participation_in_europe_africa |website=1914–1918 Online |access-date=19 August 2018 |archive-url=https://web.archive.org/web/20180819114736/https://encyclopedia.1914-1918-online.net/article/colonial_military_participation_in_europe_africa |archive-date=19 August 2018 |url-status=live }}</ref> Colonial troops also fought at [[Gallipoli Campaign|Gallipoli]], occupied [[Togo]] and [[Kamerun]] in West Africa and had a minor role in the Middle East, where France was the traditional protector of Christians in the Ottoman provinces of [[Ottoman Syria|Syria]], [[History of Palestine#Early Ottoman rule|Palestine]] and [[History of Lebanon under Ottoman rule|Lebanon]].<ref>{{cite journal |last1=Tanenbaum |first1=Jan Karl |title=France and the Arab Middle East, 1914–1920 |journal=Transactions of the American Philosophical Society |date=1978 |volume=68 |issue=7 |page=5 |doi=10.2307/1006273 |jstor=1006273 }}</ref>

===Japan===
{{Main|Japanese entry into World War I|Japan during World War I|Empire of Japan|Japanese colonial empire}}
Prior to the [[Meiji Restoration]] in 1868, Japan was a semi-feudal, largely agrarian state with few natural resources and limited technology. By 1914, it had transformed itself into a modern industrial state, with a powerful military; by defeating China in the [[First Sino-Japanese War]] during 1894–1895, it established itself as the primary power in East Asia and colonised the then-unified Korea and [[Republic of Formosa|Formosa, now modern Taiwan]].

Concerned by Russian expansion in Korea and [[Manchuria]], Britain and Japan signed the [[Anglo-Japanese Alliance]] on 30 January 1902, agreeing if either were attacked by a third party, the other would remain neutral and if attacked by two or more opponents, the other would come to its aid. This meant Japan could rely on British support in a war with Russia, if either France or Germany, which also had interests in China, decided to join them.<ref>{{cite journal |last1=Cavendish |first1=Richard |title=The 1902 Anglo-Japanese Alliance |journal=History Today |date=January 2002 |volume=52 |issue=1 |url=https://www.historytoday.com/richard-cavendish/anglo-japanese-treaty-alliance |access-date=15 August 2018 |archive-url=https://web.archive.org/web/20180816025531/https://www.historytoday.com/richard-cavendish/anglo-japanese-treaty-alliance |archive-date=16 August 2018 |url-status=live }}</ref> This gave Japan the reassurance needed to take on Russia in the 1905 [[Russo-Japanese War]]; victory established Japan in the Chinese province of [[Manchuria]].
[[File:Wakamiya.jpg|thumb|200px|The Japanese carrier [[Japanese seaplane carrier Wakamiya|''Wakamiya'']] conducted the first ship-launched aerial attack in 1914.]]
With Japan as an ally in the Far East, [[John Fisher, 1st Baron Fisher|John Fisher]], [[First Sea Lord]] from 1904 to 1910, was able to refocus British naval resources in the [[North Sea]] to counter the threat from the [[Imperial German Navy]]. The Alliance was renewed in 1911; in 1914, Japan joined the Entente in return for German territories in the Pacific, greatly annoying the Australian government which also wanted them.{{sfn|Gilbert|1995|p=123}}

On 7 August 1914, Britain officially asked for assistance in destroying German naval units in China and Japan formally declared war on Germany on 23 August 1914, followed by Austria-Hungary on 25 August 1914.<ref>{{Cite web|url=https://www.loc.gov/law/help/digitized-books/world-war-i-declarations/ww1-gazettes/Japan-1-OCR-SPLIT.pdf|title=宣戦の詔書 [Sensen no shōsho, Imperial Rescript on Declaration of War] (Aug. 23, 1914), Kanpō, Extra ed.|website=[[Library of Congress]]|archive-url=https://web.archive.org/web/20170901023644/https://www.loc.gov/law/help/digitized-books/world-war-i-declarations/ww1-gazettes/Japan-1-OCR-SPLIT.pdf|archive-date=1 September 2017|url-status=live}}</ref> On 2 September 1914, Japanese forces surrounded the German [[Treaty ports|Treaty Port]] of [[Qingdao]], then known as Tsingtao, which surrendered on 7 November. The [[Imperial Japanese Navy]] simultaneously occupied German colonies in the [[Mariana Islands|Mariana]], [[Caroline Islands|Caroline]], and [[Marshall Islands]], while in 1917, a Japanese naval squadron was sent to support the Allies in the [[Mediterranean Sea]].{{sfn|Gilbert|1995|p=329}}

Japan's primary interest was in China and in January 1915, the Chinese government was presented with a secret ultimatum of [[Twenty-One Demands]], demanding extensive economic and political concessions. While these were eventually modified, the result was a surge of anti-Japanese [[nationalism]] in China and an economic boycott of Japanese goods.<ref>Zhitian Luo, "National humiliation and national assertion-The Chinese response to the twenty-one demands", ''Modern Asian Studies'' (1993) 27#2 pp 297–319.</ref> In addition, the other Allies now saw Japan as a threat, rather than a partner, lead to tensions first with Russia, then the US after it entered the war in April 1917. Despite protests from the other Allies, after the war Japan refused to return Qingdao and the province of [[Shandong]] to China.{{sfn|Gilbert|1995|p=522}}

===Italy===
{{Main|Italian entry into World War I|Kingdom of Italy|Italian Empire}}
[[File:1917 921a Alpini.jpg|thumb|[[Alpini]] troops marching in the snow at 3,000 m altitude, 1917]]
The 1882 [[Triple Alliance (1882)|Triple Alliance]] between Germany, Austria-Hungary and Italy was renewed at regular intervals, but was compromised by conflicting objectives between Italy and Austria in the [[Adriatic Sea|Adriatic]] and [[Aegean Sea|Aegean]] seas. Italian nationalists referred to Austrian-held [[Istria]] (including [[Trieste]] and [[Rijeka|Fiume]]) and [[Trento]] as [[Italian irredentism|'the lost territories']], making the Alliance so controversial that the terms were kept secret until it expired in 1915.<ref>{{cite book |last1=Thompson |first1=Mark |title=The White War |date=2008 |publisher=Faber |isbn=978-0-571-22334-3 |pages=13–14}}</ref>

[[Alberto Pollio]], the pro-Austrian [[Chief of Staff of the Italian Army]], died on 1 July 1914, taking many of the prospects for Italian support with him.<ref>{{cite book |last1=Thompson |first1=Mark |title=The White War |date=2008 |publisher=Faber |isbn=978-0-571-22334-3 |page=22}}</ref> The Italian Prime Minister [[Antonio Salandra]] argued that as the Alliance was defensive in nature, Austria's aggression against Serbia and Italy's exclusion from the decision-making process meant it was not obliged to join them.<ref name="Hamilton, Richard F 1917. P194">Hamilton, Richard F; Herwig, Holger H. ''Decisions for War, 1914–1917''. p. 194.</ref>

His caution was understandable because France and Britain either supplied or controlled the import of most of Italy's raw materials, including 90% of its coal.<ref name="Hamilton, Richard F 1917. P194"/> Salandra described the process of choosing a side as 'sacred egoism,' but as the war was expected to end before mid-1915 at the latest, making this decision became increasingly urgent.<ref>{{cite book |last1=Clark |first1=Mark |title=Modern Italy, 1871 to the Present (Longman History of Italy) |date=2008 |publisher=Routledge |isbn=978-1-4058-2352-4 |page=219}}</ref> In line with Italy's obligations under the Triple Alliance, the bulk of the army was concentrated on Italy's border with France; in October, Pollio's replacement, [[Luigi Cadorna|General Luigi Cadorna]], was ordered to begin moving these troops to the North-Eastern one with Austria.<ref>{{cite book |last1=Thompson |first1=Mark |title=The White War |date=2008 |publisher=Faber |isbn=978-0-571-22334-3 |page=23}}</ref>

Under the April 1915 [[Treaty of London (1915)|Treaty of London]], Italy agreed to join the Entente in return for Italian-populated territories of Austria-Hungary and other concessions; in return, it declared war on Austria-Hungary in May 1915 as required, although not on Germany until 1916.<ref name="Hamilton, Richard F 1917. P194-198">Hamilton, Richard F; Herwig, Holger H. ''Decisions for War, 1914–1917''. pp. 194–198.</ref> Italian resentment at the difference between the promises of 1915 and the actual results of the 1919 [[Treaty of Versailles]] would be powerful factors in the rise of [[Benito Mussolini]].<ref>{{cite book |last1=Thompson |first1=Mark |title=The White War |date=2008 |publisher=Faber |isbn=978-0-571-22334-3 |pages=378–382}}</ref>

==Affiliated state combatants==
===Serbia===
{{Main|Kingdom of Serbia|Serbian campaign}}

In 1817, the [[Principality of Serbia]] became an autonomous province within the [[Ottoman Empire]]; with Russian support, it gained full independence after the 1877–1878 [[Russo-Turkish War (1877–1878)|Russo-Turkish War]]. Many Serbs viewed Russia as protector of the [[South Slavs]] in general but also specifically against Bulgaria, where Russian objectives increasingly collided with [[Bulgarian nationalism]].<ref>{{cite book |last1=Roudometof |first1=Victor |title=Nationalism, Globalization, and Orthodoxy: The Social Origins of Ethnic Conflict in the Balkans |date=2001 |publisher=Praeger Publishing |isbn=978-0-313-31949-5 |page=79}}</ref>

When Austria annexed Bosnia and Herzegovina in 1908, Russia responded by creating the [[Balkan League]] to prevent further Austrian expansion.<ref name=":0" /> Austria viewed Serbia with hostility partly due to its links with Russia, whose claim to be the protector of South Slavs extended to those within the Austro-Hungarian Empire, such as the [[Czechs]] and [[Slovaks]]. Serbia also potentially gave Russia the ability to achieve their long-held objective of capturing [[Constantinople]] and the [[Dardanelles]].<ref name="The Freedom of the Straits"/>
[[File:Serbian retreat WWI.jpg|thumb|200px|The Serbian Army in retreat, 1915]]
Austria-Hungary supported the idea of an [[independent Albania]], since this would prevent Serbian access to the Austrian-controlled [[Adriatic Sea]].<ref>{{cite book |last1=Clark |first1=Christopher |title=The Sleepwalkers |date=2013 |publisher=Harper |isbn=978-0-06-114665-7 |pages=[https://archive.org/details/isbn_9780061146657/page/282 282–283] |url=https://archive.org/details/isbn_9780061146657/page/282 }}</ref> The success of the [[Albanian revolt of 1912|Albanian revolt in 1912]] threatened Serbian ambitions for the incorporation of "[[Old Serbia]]" into its domain and exposed the weakness of the Ottoman Empire. This led to the outbreak of the [[First Balkan War]], with [[Kingdom of Serbia|Serbia]], [[Kingdom of Montenegro|Montenegro]], [[Kingdom of Bulgaria|Bulgaria]] and [[Kingdom of Greece|Greece]] capturing most of the remaining Ottoman possessions in Europe. Disputes over the division of these resulted in the [[Second Balkan War]], in which Bulgaria was comprehensively defeated by its former allies.

As a result of the 1913 [[Treaty of Bucharest (1913)|Treaty of Bucharest]], Serbia increased its territory by 100% and its population by 64%.<ref>{{cite book |last1=Clark |first1=Christopher |title=The Sleepwalkers |date=2013 |publisher=Harper |isbn=978-0-06-114665-7 |page=[https://archive.org/details/isbn_9780061146657/page/285 285] |url=https://archive.org/details/isbn_9780061146657/page/285 }}</ref> However, it now faced a hostile Austria-Hungary, a resentful Bulgaria and [[Ohrid–Debar uprising|resistance in its conquered territories]]. Germany too had ambitions in the Ottoman Empire, the centrepiece being the planned [[Berlin–Baghdad railway]], with Serbia the only section not controlled by a pro-German state.

The exact role played by Serbian officials in the [[assassination of Archduke Franz Ferdinand]] is still debated but despite complying with most of their demands, Austria-Hungary invaded on 28 July 1914. While Serbia successfully repulsed the Austro-Hungarian army in 1914, it was exhausted by the two Balkan Wars and unable to replace its losses of men and equipment. In 1915, Bulgaria joined the Central Powers and by the end of the year, a combined Bulgar-Austrian-German army occupied most of Serbia. Between 1914 and 1918, Serbia suffered the greatest proportional losses of any combatant, with over 25% of all those mobilised becoming casualties; including civilians and deaths from disease, over 1.2&nbsp;million died, nearly 30% of the entire population.

===Belgium===
{{main|Belgium|Belgian colonial empire}}
{{see also|Belgian government at Sainte-Adresse}}
In 1830, the southern provinces of the Netherlands broke away to form the [[Belgium|Kingdom of Belgium]] and their independence was confirmed by the 1839 [[Treaty of London (1839)|Treaty of London]]. Article VII of the Treaty required Belgium to remain perpetually neutral and committed Austria, France, Germany and Russia to guarantee that against aggression by any other state, including the signatories.<ref>{{cite book |last1=Hull |first1=Isabel V |title=A Scrap of Paper: Breaking and Making International Law during the Great War |date=2014 |publisher=Cornell University |isbn=978-0-8014-5273-4 |pages=Chapter 2 Belgian Neutrality}}</ref>
[[File:Le Front de l'Yser (Flandre) par Georges-Émile Lebacq.jpg|thumb|left|200px|The [[Yser Front]], 1917 by Belgian artist [[Georges Lebacq|Georges-Émile Lebacq]]]]
[[File:Congo belge campagne 1918.jpg|thumb|200px|Belgian Congolese ''Force Publique'' troops in [[German East Africa]], 1916]]
While the French and German militaries accepted Germany would almost certainly violate Belgian neutrality in the event of war, the extent of that was unclear. The original [[Schlieffen Plan]] only required a limited incursion into the Belgian [[Ardennes]], rather than a full-scale invasion; in September 1911, the Belgian Foreign Minister told a British Embassy official they would not call for assistance if the Germans limited themselves to that.<ref name=":1" /> While neither Britain or France could allow Germany to occupy Belgium unopposed, a Belgian refusal to ask for help would complicate matters for the [[Liberal government, 1905–1915|British Liberal government]], which contained a significant isolationist element.

However, the key German objective was to avoid war on two fronts; France had to be defeated before Russia could fully mobilise and give time for German forces to be transferred to the East. The growth of the Russian railway network and increase in speed of mobilisation made rapid victory over France even more important; to accommodate the additional 170,000 troops approved by the 1913 Army Bill, the 'incursion' now became a full-scale invasion. The Germans accepted the risk of British intervention; in common with most of Europe, they expected it to be a short war while their London Ambassador claimed civil war in Ireland would prevent Britain from assisting its Entente partners.<ref name="auto"/>

On 3 August, a German ultimatum demanded unimpeded progress through any part of Belgium, which was refused. Early on the morning of 4 August, the Germans invaded and the Belgian government called for British assistance under the 1839 Treaty; by the end of 1914, over 95% of the country was occupied but the Belgian Army held their lines on the [[Yser Front]] throughout the war.

In the [[Belgian Congo]], 25,000 Congolese troops plus an estimated 260,000 porters joined British forces in the 1916 [[East African Campaign (World War I)|East African Campaign]].<ref>{{cite book |last1=van Reybrouck |first1=David |title=Congo: The Epic History of a People |date=2014 |publisher=Harper Collins |isbn=978-0-06-220012-9 |pages=132 passim}}</ref> By 1917, they controlled the western part of [[German East Africa]] which would become the Belgian [[League of Nations mandate|League of Nations Mandate]] of [[Ruanda-Urundi]] or modern-day [[Rwanda]] and [[Burundi]].<ref>{{cite book |last1=Strachan |first1=Hew |title=First World War; a New History |date=2014 |publisher=Simon & Schuster UK |isbn=978-1-4711-3426-5 |page=70}}</ref>

===Greece===
{{Main|Kingdom of Greece|Greece during World War I}}
[[File:158 14 Constantin Venizelos.jpg|thumb|left|150px|[[Eleftherios Venizelos]] with [[Constantine I of Greece|Constantine]] during the [[Balkan Wars]]]]
[[File:A Salonique, le défilé du premier bataillon grec volontaire.jpg|thumb|200px|A unit of the [[National Defence Army Corps]] on its way to the front in 1918]]
Greece almost doubled in size as a result of the [[Balkan Wars]] of 1912 and 1913, but the success masked deep divisions within the political elite. In 1908, the island of [[Crete]], formally part of the [[Ottoman Empire]] but administered by Greek officials, declared union with Greece, led by the charismatic nationalist [[Eleftherios Venizelos]]. A year later, young army officers formed the Military League to advocate for an aggressive and expansionist foreign policy; with their backing, Venizelos won a majority in the 1910 Parliamentary elections, followed by another in 1912.<ref>{{cite journal |last1=Mazower |first1=Mark |title=The Messiah and the Bourgeoisie: Venizelos and Politics in Greece, 1909 – 1912 |journal=The Historical Journal |date=December 1992 |volume=35 |issue=4 |page=886 |doi=10.1017/S0018246X00026200 |jstor=2639443 |s2cid=154495315 }}</ref> He had effectively broken the power of the pre-1910 political class and his position was then further strengthened by success in the Balkan Wars.

In 1913, the Greek monarch [[George I of Greece|George I]] was assassinated; he was succeeded by his son [[Constantine I of Greece|Constantine]] who had attended [[Heidelberg University]], served in a Prussian regiment and married [[Sophia of Prussia]], sister of Emperor [[Wilhelm II, German Emperor|William II]]. These links and a belief the Central Powers would win the war combined to make Constantine pro-German.<ref name="Routledge">{{cite book |editor1=Tucker, Spencer C |author=Mitchell, Dennis J |title=The European Powers in the First World War: An Encyclopedia |date=1996 |publisher=Routledge |isbn=978-0-8153-0399-2 |pages=195–196 |url=https://books.google.com/books?id=gv3GEyB19wIC&q=the+assassination+of+george+i+of+greece&pg=PA196 |access-date=2 September 2018 |archive-url=https://web.archive.org/web/20180903215551/https://books.google.co.uk/books?id=gv3GEyB19wIC&pg=PA196#v=onepage&q=the%20assassination%20of%20george%20i%20of%20greece |archive-date=3 September 2018 |url-status=live}}</ref> Venizelos himself favoured the Entente, partly due to their ability to block the maritime trade routes required for Greek imports.
[[File:Colonel Christodoulou interrogates Bulgarian POWs.jpg|thumb|180px|Colonel [[Nikolaos Christodoulou]] of the National Defence Army Corps interrogating Bulgarian prisoners, September 1918]]
Other issues adding complexity to this decision included disputes with Bulgaria and Serbia over the regions of [[Thrace]] and [[Macedonia (region)|Macedonia]] as well as control of the [[Aegean Islands]]. Greece captured most of the islands during the Balkan Wars but Italy occupied the [[Dodecanese]] in 1912 and was in no hurry to give them back, while the Ottomans demanded the return of many others.<ref>{{cite journal |last1=Kaldis |first1=William Peter |title=Background for Conflict: Greece, Turkey, and the Aegean Islands, 1912–1914 |journal=The Journal of Modern History |date=June 1979 |volume=51 |issue=2 |pages=D1119–D1146 |jstor=1881125 |doi=10.1086/242039 |s2cid=144142861 }}</ref> In general, the Triple Entente favoured Greece, the Triple Alliance backed the Ottomans; Greece ultimately gained the vast majority but Italy did not cede the Dodecanese until 1947, while others remain [[Aegean dispute|disputed]] even today.

As a result, Greece initially remained neutral but in March 1915, the Entente offered concessions to join the [[Dardanelles]] campaign. Arguments over whether to accept led to the [[National Schism]], with an Entente-backed administration under Venizelos in Crete, and a Royalist one led by Constantine in [[Athens]] that supported the Central Powers.<ref name="Routledge"/>

In September 1915, Bulgaria joined the Central Powers; in October, Venizelos allowed Entente forces to land at [[Thessaloniki|Thessaloniki or Salonica]] to support the Serbs, although they were too late to prevent their defeat. In August 1916, Bulgarian troops advanced into Greek-held Macedonia and Constantine ordered the army not to resist; anger at this led to a coup and he was eventually forced into exile in June 1917. A new national government under Venizelos joined the Entente, while the Greek [[National Defence Army Corps]] fought with the Allies on the [[Macedonian front]].

===Montenegro===
{{Main|Kingdom of Montenegro}}
[[File:Skadar predaja zastave.jpg|thumb|250px|left|[[Nicholas I of Montenegro|Nicholas I]] accepting the surrender of Scutari, April 1913; Montenegro's major gain from the Balkan War, it was relinquished several months later]]
Unlike Serbia, with whom it shared close cultural and political connections, the [[Kingdom of Montenegro]] gained little from its participation in the 1912–1913 Balkan Wars. The main Montenegrin offensive was in [[Albanian Vilayet|Ottoman-controlled Albania]], where it suffered heavy losses during the seven month [[Siege of Scutari (1912–13)|Siege of Scutari]]. Austria-Hungary opposed Serb or Montenegrin control of Albania, since it provided access to the [[Adriatic Sea]]; despite Scutari's surrender, Montenegro was forced to relinquish it by the [[Treaty of London (1913)|1913 Treaty of London]] and it became capital of the short-lived [[Principality of Albania]].<ref>{{cite book |last1=Treadway |first1=John |title=The Falcon and the Eagle: Montenegro and Austria-Hungary, 1908–14 |date=1983 |publisher=Purdue Press |isbn=978-0-911198-65-2 |pages=150–153}}</ref> This was largely an Austrian creation; the new ruler, [[William, Prince of Albania]], was a German who was forced into exile in September, only seven months after taking up his new position and later served with the [[Imperial German Army]].<ref>{{cite book|last=Elsie|first=Robert|page=255|author-link=Robert Elsie|title=Historical Dictionary of Albania|volume=75|publisher=Scarecrow Press|year=2010|edition=2|series=Historical Dictionaries of Europe|isbn=978-0810861886}}</ref>

[[File:M113 11a soldat montenégrins partant au front Lovcen, Cettinié.jpg|thumb|250px|Montenegrin soldiers leaving for the front, October 1914]]
In addition to the lack of substantive gains from the Balkan Wars, there were long-running internal divisions between those who like [[Nicholas I of Montenegro|Nicholas I]] preferred an independent Montenegro and those who advocated union with Serbia. In July 1914, Montenegro was not only militarily and economically exhausted, but also faced a multitude of political, economic and social issues.<ref name="Montenegro">{{cite web |last1=Raspopović |first1=Radoslav |title=Montenegro |url=https://encyclopedia.1914-1918-online.net/article/montenegro |website=encyclopedia.1914-1918-online |access-date=5 September 2018 |archive-url=https://web.archive.org/web/20180906014025/https://encyclopedia.1914-1918-online.net/article/montenegro |archive-date=6 September 2018 |url-status=live }}</ref>

At meetings held in March 1914, Austria-Hungary and Germany agreed union with Serbia must be prevented; Montenegro could either remain independent or be divided, its coastal areas becoming part of Albania, while the rest could join Serbia.<ref name="Montenegro"/>

Nicholas seriously considered neutrality as a way to preserve his dynasty and on 31 July notified the Russian Ambassador Montenegro would only respond to an Austrian attack. He also held discussions with Austria, proposing neutrality or even active support in return for territorial concessions in Albania.<ref>{{cite book |last1=Treadway |first1=John |title=The Falcon and the Eagle: Montenegro and Austria-Hungary, 1908–14 |date=1983 |publisher=Purdue Press |isbn=978-0-911198-65-2 |pages=186–189}}</ref>

However, close links between the Serbian and Montenegrin militaries as well as popular sentiment meant there was little support for remaining neutral, especially after Russia joined the war; on 1 August, the National Assembly declared war on Austria-Hungary in fulfilment of its obligations to Serbia. After some initial success, in January 1916, the Montenegrin Army was forced to surrender to an Austro-Hungarian force.

=== Beda ===
The [[Beda Sultanate]] was invaded by Ottoman forces in February 1915 and March 1916.<ref name=":2">{{Cite book|last=Mehra|first=Ram Narain|url=https://books.google.com/books?id=cVSPGAAACAAJ|title=Aden & Yemen, 1905–1919|date=1988|publisher=Agam Prakashan|pages=125, 159|language=en}}</ref> Britain assisted the Beda Sultanate in defeating the Ottoman invasions by sending arms and ammunition.<ref name=":7">{{Cite book|url=https://books.google.com/books?id=X_otAQAAIAAJ|title=Records of Yemen, 1797–1960: 1950–1954|date=1993|publisher=Archive Editions|pages=397|isbn=978-1852073701|language=en}}</ref>

===Asir===
The [[Idrisid Emirate of Asir]] participated in the [[Arab Revolt]]. Its Emir, [[Muhammad ibn Ali al-Idrisi]], signed an agreement with the British and joined the Allies in May 1915.

===Nejd and Hasa===
The [[Emirate of Nejd and Hasa]] [[Battle of Jarrab|launched a failed offensive against the Ottoman aligned Emirate of Jabal Shammar in January 1915]]. It then agreed to enter the war as an ally of Britain in the [[Treaty of Darin]] on 26 December 1915.<ref>{{cite book |title=Memoirs |last=[[Abdullah I of Jordan]] |author2=Philip Perceval Graves |author-link2=Philip Graves |year=1950 |page=186}}</ref>

===Romania===
{{Main|Kingdom of Romania|Romanian Old Kingdom|Romania in World War I}}
[[File:Mortier Negrei 250 mm Model 1916.JPG|thumb|left|150px|Romanian 250 mm Negrei Model 1916 mortar at the [[National Military Museum, Romania|National Military Museum]]]]
[[File:A Vlaicu III 02.png|thumb|Vlaicu III]]
[[File:Romanian troops at Marasesti in 1917.jpg|thumb|150px|Romanian troops at Mărășești]]
Equal status with the main Entente Powers was one of the primary conditions for Romania's entry into the War. The Powers officially recognised this status through the [[Treaty of Bucharest (1916)|1916 Treaty of Bucharest]].<ref>{{cite book|first = Charles Upson|last = Clark|title = United Roumania|page = 135|date = 1971|publisher = Arno Press|isbn= 978-0405027413}}</ref> Romania fought on three of the four European Fronts: [[Eastern Front (World War I)|Eastern]], [[Balkans Campaign (World War I)|Balkan]] and [[Italian Front (World War I)|Italian]], fielding in total over 1,200,000 troops.<ref>Spencer C. Tucker, Priscilla Mary Roberts, ''Encyclopedia of World War I'', p. 273</ref>

Romanian military industry was mainly focused on converting various fortification guns into field and anti-aircraft artillery. Up to 334 German 53&nbsp;mm [[Fahrpanzer]] guns, 93 French 57&nbsp;mm Hotchkiss guns, 66 Krupp 150&nbsp;mm guns, and dozens more 210&nbsp;mm guns were mounted on Romanian-built [[Gun carriage|carriages]] and transformed into mobile field artillery, with 45 Krupp 75&nbsp;mm guns and 132 Hotchkiss 57&nbsp;mm guns being transformed into anti-aircraft artillery. The Romanians also [[10.5&nbsp;cm Feldhaubitze M.12|upgraded 120 German Krupp 105&nbsp;mm howitzers]], the result being the most effective field howitzer in Europe at that time. Romania even managed to design and build from scratch its own model of mortar, the 250&nbsp;mm Negrei Model 1916.<ref>Adrian Storea, Gheorghe Băjenaru, ''Artileria română în date și imagini (Romanian artillery in data and pictures)'', pp. 40, 49, 50, 54, 59, 61, 63, 65, and 66 (in Romanian)</ref>

Other Romanian technological assets include the building of [[A Vlaicu III|Vlaicu III]], the world's first aircraft made of metal.<ref>Jozef Wilczynski, ''Technology in Comecon: Acceleration of Technological Progress Through Economic Planning and the Market'', p. 243</ref> The Romanian Navy possessed the largest warships on the Danube. They were a class of four river monitors, built locally at the [[Galați shipyard]] using parts manufactured in Austria-Hungary. The first one launched was ''Lascăr Catargiu'', in 1907.<ref>International Naval Research Organization, ''Warship International, Volume 21'', p. 160</ref><ref>Frederick Thomas Jane, ''Jane's Fighting Ships'', p. 343{{full citation needed|date=September 2021}}</ref> The Romanian monitors displaced almost 700 tons, were armed with three 120&nbsp;mm naval guns in three turrets, two 120&nbsp;mm naval howitzers, four 47&nbsp;mm anti-aircraft guns and two 6.5 machine guns.<ref>Robert Gardiner, ''Conway's All the World Fighting Ships 1906–1921'', p. 422</ref> The monitors took part in the [[Battle of Turtucaia]] and the [[First Battle of Cobadin]]. The Romanian-designed Schneider 150&nbsp;mm Model 1912 howitzer was considered one of the most modern field guns on the Western Front.<ref>Adrian Storea, Gheorghe Băjenaru, ''Artileria română în date și imagini (Romanian artillery in data and pictures)'', p. 53 (in Romanian)</ref>

Romania's entry into the War in August 1916 provoked major changes for the Germans. General [[Erich von Falkenhayn]] was dismissed and sent to command the Central Powers forces in Romania, which enabled [[Paul von Hindenburg|Hindenburg]]'s subsequent ascension to power.{{sfn|Gilbert|1995|p=282}} Due to having to fight against all of the Central Powers on the longest front in Europe (1,600&nbsp;km) and with little foreign help (only 50,000 Russians aided 650,000 Romanians in 1916),<ref>{{cite book|first = Glenn E.|last = Torrey|title = Romania and World War I|page = 58|date = 1998|publisher = Center for Romanian Studies|isbn = 978-9739839167}}</ref> [[Battle of Bucharest|the Romanian capital was conquered]] that December. Vlaicu III was also captured and shipped to Germany, being last seen in 1942.<ref>Michael Hundertmark, Holger Steinle, ''Phoenix aus der Asche – Die Deutsche Luftfahrt Sammlung Berlin'', pp. 110–114 (in German)</ref> The Romanian administration established a new capital at [[Iași]] and continued to fight on the Allied side in 1917.<ref>''România în anii primului război mondial (Romania in the years of the First World War), Volume II'', p. 830 (in Romanian)</ref> Despite being relatively short, the Romanian campaign of 1916 provided considerable respite for the Western Allies, as the Germans ceased all their other offensive operations in order to deal with Romania.{{sfn|Gilbert|1995|p=287}} After suffering a tactical defeat against the Romanians (aided by Russians) in July 1917 at [[Battle of Mărăști|Mărăști]], the Central Powers launched two counterattacks, at [[Battle of Mărășești|Mărășești]] and [[Third Battle of Oituz|Oituz]]. The German offensive at Mărășești was soundly defeated, with German prisoners later telling their Romanian captors that German casualties were extremely heavy, and that they "had not encountered such stiff resistance since the battles of Somme and Verdun".<ref>{{cite book|title =King of Battle: Artillery in World War I|page = 347|url = https://books.google.com/books?id=0fGcCwAAQBAJ&pg=PA347|publisher = Brill|date = 2016|isbn =978-9004307285}}</ref> The Austro-Hungarian offensive at Oituz also failed. On 22 September, the Austro-Hungarian [[Enns-class river monitor|''Enns''-class]] river monitor [[SMS Inn|SMS ''Inn'']] was sunk by a Romanian mine near Brăila.<ref>{{cite book|first = Angus|last = Konstam|title =Gunboats of World War I|page = 29|publisher = Bloomsbury Publishing|date = 2015|isbn = 978-1472804990}}</ref><ref>{{cite book|first = René |last =Greger |title =Austro-Hungarian warships of World War I|page= 142|publisher = Allan|date = 1976|isbn = 978-0711006232}}</ref> After Russia signed the [[Treaty of Brest-Litovsk]] and dropped out of the War, Romania was left surrounded by the Central Powers and eventually signed a [[Treaty of Bucharest (1918)|similar treaty]] on 7 May 1918. Despite being forced to cede land to Austria-Hungary and Bulgaria, Romania ended up with a net gain in territory due to the [[Union of Bessarabia with Romania|Union with Bessarabia]]. On 10 November, Romania re-entered the War and fought a [[Hungarian-Romanian War|war with Hungary]] that lasted until August 1919.

===Republic of the United States of Brazil===
{{Main|Brazil during World War I}}
[[File:Brazilian Soldiers First War.jpg|thumb|Brazilian soldiers in World War I]]

Brazil entered the war in 1917 after the United States intervened on the basis of Germany's unrestricted submarine warfare sinking its merchant ships, which Brazil also cited as a reason to enter the war fighting against Germany and the Central Powers. The [[First Brazilian Republic]] sent the Naval Division in War Operations that joined the British fleet in [[Gibraltar]] and made the first Brazilian naval effort in international waters. In compliance with the commitments made at the [[Pan-American Conference|Inter-American Conference]], held in Paris from 20 November to 3 December 1917, the Brazilian Government sent a medical mission composed of civilian and military surgeons to work in field hospitals of the European theatre, a contingent of sergeants and officers to serve with the [[French Army]]; Airmen from the Army and Navy to join the [[Royal Air Force]], and the employment of part of the Fleet, primarily in the anti-submarine war.

==Co-belligerents: the United States==
{{Main|United States in World War I}}
[[File:Council of Four Versailles.jpg|thumb|[[Big Four (World War I)|The Council of Four]] (from left to right): [[David Lloyd George]], [[Vittorio Emanuele Orlando]], [[Georges Clemenceau]], and [[Woodrow Wilson]] in Versailles, 1919]]
The [[United States]] declared war on Germany in April 1917 on the grounds that Germany violated US neutrality by attacking international shipping with its [[unrestricted submarine warfare]] campaign.<ref name="US Declaration of War">{{cite web|url=http://www.firstworldwar.com/source/usawardeclaration.htm|title=First World War.com – Primary Documents – U.S. Declaration of War with Germany, 2 April 1917|access-date=12 May 2008|archive-url=https://web.archive.org/web/20080516015730/http://www.firstworldwar.com/source/usawardeclaration.htm|archive-date=16 May 2008|url-status=live}}</ref> The remotely connected [[Zimmermann Telegram]] of the same period, within which the Germans promised to help Mexico regain some of its territory [[Mexican Cession|lost to the US]] nearly seven decades before in the event of the United States entering the war, was [[Zimmermann Telegram#U.S. response|also a contributing factor]]. [[American entry into World War I|The US entered the war]] as an "associated power", rather than a formal ally of [[French Third Republic|France]] and the [[United Kingdom of Great Britain and Ireland|United Kingdom]], in order to avoid "foreign entanglements".<ref name="Tucker&Roberts pp. 1232, 1264">Tucker&Roberts pp. 1232, 1264, 1559</ref> Although the [[Ottoman Empire]] and [[Kingdom of Bulgaria|Bulgaria]] severed relations with the United States, neither declared war,<ref name="Tucker&Roberts p. 1559">Tucker&Roberts p. 1559</ref> nor did [[Austria-Hungary]]. Eventually, however, the United States also [[United States declaration of war on Austria-Hungary|declared war on Austria-Hungary]] in December 1917, predominantly to help hard-pressed Italy.

==Non-state combatants==
Three non-state combatants, which voluntarily fought with the Allies and seceded from the constituent states of the Central Powers at the end of the war, were allowed to participate as winning nations to the peace treaties:{{Citation needed|date=January 2016}}
* {{flagicon|First Republic of Armenia}} [[First Republic of Armenia|Armenian]] [[Armenian fedayi|irregulars]] and [[Armenian volunteer units|volunteers]]: seceded from the Russian Empire in the aftermath of the Russian Revolution and fought against the Ottoman Empire
* [[File:Flag of the Assyrian Volunteers.svg|border|20px]] [[Assyrian volunteers]] under [[Shimun XIX Benyamin|Mar Shimun XIX Benyamin]] and the Assyrian tribal chiefs decided to side with the Allies, first with Russia, and next with the British, in the hope that they might secure after the victory, self-government for the Assyrians.<ref>{{cite book|url = http://www.aina.org/books/bbota.htm |first =Yusuf|last = Malek|title = The British Betrayal of the Assyrians |date =1935|publisher =Assyrian International News Agency}}</ref> The French also joined the alliance with the Assyrians, offering them 20,000 rifles, and the Assyrian army grew to 20,000 men co-led by [[Agha Petros]] of the Bit-[[Baz (tribe)|Bazi]] tribe, and [[Malik Khoshaba]] of the Bit-[[Tyari|Tiyari]] tribe.<ref name="ReferenceA">Paul Bartrop, Encountering Genocide: Personal Accounts from Victims, Perpetrators, and Witnesses, ABC-CLIO, 2014</ref><ref>{{Cite web|url=https://books.google.com/books?id=hokGAQAAIAAJ&q=Agha+Petrus++Malik+Khochaba&pg=PA281|title=Shall this Nation Die?|first=Joseph|last=Naayem|date=30 July 1921|publisher=Chaldean rescue|via=Google Books}}</ref>
* {{flagicon|Second Polish Republic|1919}} [[Polish Legions in World War I|Polish Legions]]
* {{flagicon|Bohemia}} [[Czechoslovak Legion]]s: armed by [[Czechoslovak Legion in France|France]], [[Czechoslovak Legion in Italy|Italy]], and Russia
Additionally, there were also several [[Kurdish rebellions during World War I]]. Most of these, except for the uprisings of August 1917, were not supported by any of the Allied powers.<ref>{{Cite web|url=http://etheses.lse.ac.uk/2625/1/U615574.pdf|title=Britain's Policy Towards The Kurdish Question, 1915–1923|last=Eskander|first=Saad|website=etheses.lse.ac.uk|page=45}}</ref>

==Leaders==
{{Main|Allied leaders of World War I}}
[[File:General of War.jpg|thumb|250px|Military leaders of World War I: [[Jules Jacques de Dixmude]] (Belgium), [[Armando Diaz]] (Italy), [[Ferdinand Foch]] (France), [[John J. Pershing|John Pershing]] (United States), and [[David Beatty, 1st Earl Beatty|David Beatty]] (United Kingdom)]]
[[File:Marshal Foch victory-harmony banner June 8 1919.jpg|thumb|300px|alt=Collection of flags|Marshal Foch's Victory-Harmony Banner]]

===Serbia===
* [[Peter I of Serbia|Peter I]] – [[List of Serbian monarchs|King of Serbia]]
* [[Alexander I of Yugoslavia|Crown Prince Alexander]] – Regent, Commander-in-Chief
* [[Nikola Pašić]] – [[Prime Minister of Serbia]]
* [[Vojvoda (Serbia and Yugoslavia)|Field Marshal]] [[Radomir Putnik]] – [[Chief of the Serbian General Staff|Chief of the General Staff]] of the [[Serbian Army]] (1914–1915)
* General/Field Marshal [[Živojin Mišić]] – Deputy Chief of the General Staff (1914), Commander of [[First Army (Serbia)|First Army]] (1914–1915; 1917), later Chief of the General Staff (1918)
* General/[[Field marshal (Serbia and Yugoslavia)|Field Marshal]] [[Petar Bojović]] – Commander of the [[First Army (Serbia)|First Army]] (1914), Deputy Chief of General Staff (1915–1916), Chief of the General Staff (1916–1917) later Commander of the First Army (1918)
* General/[[Field marshal (Serbia and Yugoslavia)|Field Marshal]] [[Stepa Stepanović]] – Commander of the [[Second Army (Serbia)|Second Army]] (1914–1918)
* General [[Pavle Jurišić Šturm]] – Commander of the [[Third Army (Serbia)|Third Army]] (1914–1916)
* Colonel {{Interlanguage link|Dušan Stefanović|sr|Душан Стефановић}} – [[Ministry of Defence (Serbia)|Minister of War]] (1914)
* Colonel {{ill|Radivoje Bojović|sr}} – Minister of War (1914–1915)
* Colonel/General {{Interlanguage link|Božidar Terzić|sr|Божидар Терзић}} – Minister of War (1915–1918)
* General [[Mihailo Rašić]] – Minister of War (1918)
* Colonel/General [[Miloš Vasić (general)|Miloš Vasić]] – Commander of the First Army (1916; 1917), Commander of the Third Army (1916)

===Montenegro===
* [[Nicholas I of Montenegro|Nicholas I]] – [[List of monarchs of Montenegro|King of Montenegro]], Commander-in-Chief
* General [[Serdar (Ottoman rank)|Serdar]] [[Janko Vukotić]] – [[Prime Minister of Montenegro|Prime Minister]], Commander of the 1st Montenegrin Army
* {{flagicon|Kingdom of Serbia|size=20px}} General [[Božidar Janković (general)|Božidar Janković]] – Chief of the General Staff of the Montenegrin Army (1914–1915)
* {{flagicon|Kingdom of Serbia|size=20px}} Colonel [[Petar Pešić]] – Deputy Chief of the General Staff of the Montenegrin Army (1914–1915), later Chief of the General Staff of the Montenegrin Army (1915–1916)
* [[Danilo, Crown Prince of Montenegro|Crown Prince Danilo II Petrović-Njegoš]] – in the staff of the 1st Montenegrin Army
* Brigadier [[Krsto Popović]] – in the staff of the 1st Montenegrin Army, [[Aide-de-camp]] to Serdar Janko Vukotić
* General [[Anto Gvozdenović]] – King's Aide-de-camp
* General [[Mitar Martinović]] – commander of several detachments in the Montenegrin Army (Drina and Herzegovina detachments together in 1914–1915, Kotor detachment in 1916)

===Russia (1914–1917)===
[[File:RussianHighCommand.jpeg|thumb|Meeting of the Russian High Command]]
* [[Nicholas II of Russia|Nicholas II]] – [[Emperor of Russia|Russian Emperor]], [[List of Polish monarchs|King of Poland]], and [[Grand Duke of Finland]] (until 15 March 1917)
* [[Grand Duke Nicholas Nikolaevich of Russia (1856–1929)|Grand Duke Nicholas Nikolaevich]] – Commander-in-Chief (1 August 1914 – 5 September 1916) and viceroy in the [[Caucasus]]
* [[Ivan Goremykin]] – [[List of heads of government of Russia|Chairmen of Council of Ministers of the Russian Empire]] (1 August 1914 – 2 February 1916)
* [[Boris Shturmer|Boris Stürmer]] – Chairmen of Council of Ministers of the Russian Empire (2 February 1916 – 23 November 1916)
* [[Alexander Trepov]] – Chairmen of Council of Ministers of the Russian Empire (23 November 1916 – 27 December 1916)
* [[Nikolai Golitsyn]] – Chairmen of Council of Ministers of the Russian Empire (27 December 1916 – 9 January 1917)
* General of the Cavalry [[Alexander Samsonov]] – Commander of the [[2nd Army (Russian Empire)|Russian Second Army]] for the invasion of [[East Prussia]] (1 August 1914 – 29 August 1914)
* General of the Cavalry [[Paul von Rennenkampf]] – Commander of the [[1st Army (Russian Empire)|Russian First Army]] for the invasion of East Prussia (1 August 1914 – November 1914)
* [[General of the Artillery (Imperial Russia)|General of the Artillery]] [[Nikolai Ivanov (general)|Nikolay Ivanov]] – Commander of the Russian Army on the [[Southwestern Front (Russian Empire)|Southwestern Front]], (1 August 1914 – March 1916) responsible for much of the action in [[Galicia (Eastern Europe)|Galicia]] [[File:Aleksei Brusilov at Rivne Railway Station (October 1915).jpg|thumb|[[Aleksei Brusilov]] in Rivne, [[Volhynian Governorate]], 1915]]
* [[Adjutant general|General Adjutant]] [[Aleksei Brusilov]] – Commander of the Southwestenr Front, then provisional Commander-in-Chief after the Tsar's abdication (February 1917 – August 1917)
* [[General of the Infantry (Imperial Russia)|General of the Infantry]] [[Lavr Kornilov|Lavr Georgievich Kornilov]] – Commander of the Southwestern Front, then Commander-in-Chief (August 1917)
* General of the Infantry [[Aleksey Kuropatkin]] – Commander of the [[Northern Front (Russian Empire)|Northern Front]] (October 1915 – 1917)
* General of the Infantry [[Nikolai Yudenich]] – Commander of the Caucasus (January 1915 – May 1917)
* [[List of Russian admirals|Admiral]] [[Andrei Eberhardt]] – Commander of the [[Black Sea Fleet]] (1914–16)
* Admiral [[Alexander Kolchak]] – Commander of the Black Sea Fleet (1916–17)
* Admiral [[Nikolai Ottovich von Essen|Nikolai Essen]] – Commander of the [[Baltic Fleet]] (1913 – May 1915)

===Belgium===
* [[Albert I of Belgium]] – [[Monarchy of Belgium|King of the Belgians]] (23 December 1909 – 17 February 1934) and Commander-in-Chief of the Belgian Army
* [[Charles de Broqueville]] – [[Prime Minister of Belgium|Prime Minister]] (1912–1918); replaced by [[Gérard Cooreman]] in June 1918 shortly before the end of the war.
* [[Félix Wielemans]] – Chief of Staff of the Belgian Army
* [[Gérard Leman]] – general commanding the [[Battle of Liège|defense of Liège]]
* [[Charles Tombeur]] – commander of the colonial ''[[Force Publique]]'' in the [[East African campaign (World War I)|East African theatre]]

===France===
[[File:Le Roi George V, Le General Joffre et le President de la Republique sur le front.jpg|thumb|President [[Raymond Poincaré]] and King [[George V]], 1915]]
* [[Raymond Poincaré]] – [[President of France]]
* [[René Viviani]] – [[Prime Minister of France]] (13 June 1914 – 29 October 1915)
* [[Aristide Briand]] – Prime Minister of France (29 October 1915 – 20 March 1917)
* [[Alexandre Ribot]] – Prime Minister of France (20 March 1917 – 12 September 1917)
* [[Paul Painlevé]] – Prime Minister of France (12 September 1917 – 16 November 1917)
* [[Georges Clemenceau]] – Prime Minister of France (from 16 November 1917)
* [[Divisional general|Divisional General]]/[[Marshal of France|Marshal]] [[Joseph Joffre]] – Commander-in-Chief of the [[French Army]] (3 August 1914 – 13 December 1916)
* Divisional General [[Robert Nivelle]] – Commander-in-Chief of the French Army (13 December 1916 – April 1917)
* Divisional General/Marshal [[Philippe Pétain]] – Commander-in-Chief of the French Army (April 1917 – 11 November 1918)
* Divisional General/Marshal [[Ferdinand Foch]] – Supreme Allied Commander (26 March 1918 – 11 November 1918)
* Divisional General [[Maurice Sarrail]] – Commander of the Allied armies at the [[Macedonian front|Salonika front]] (1915–1917)
* [[Army general (France)|Army General]] [[Adolphe Guillaumat]] – Commander of the Allied armies at the Salonika front (1917–1918)
* Divisional General/Marshal [[Louis Franchet d'Espèrey]] – Commander of the Allied armies at the Salonika front (1918)
* Brigadier General [[Milan Rastislav Štefánik]] – general of the French Army, Commander of the Czechoslovak Legions

===Britain and the British Empire===
====United Kingdom====
[[File:Winston Churchill With Naval Wing of the Royal Flying Corps, 1914. CH4778.jpg|thumb|[[First Lord of the Admiralty]] [[Winston Churchill]], 1914]]
[[File:The Cooperation of the Allied Forces on the Western Front, 1914-1918 Q7179.jpg|thumb|[[Douglas Haig, 1st Earl Haig|Douglas Haig]] and [[Ferdinand Foch]] inspecting the [[Gordon Highlanders]], 1918]]
* [[George V]] – [[Monarchy of the United Kingdom|King of the United Kingdom]], and the British Dominions, [[Emperor of India]]
* [[H. H. Asquith]] – [[Prime Minister of the United Kingdom]] (until 5 December 1916)
* [[David Lloyd George]] – Prime Minister of the United Kingdom (from 7 December 1916)
* [[Field marshal (United Kingdom)|Field Marshal]] [[Herbert Kitchener, 1st Earl Kitchener|Horatio Herbert Kitchener]] – [[Secretary of State for War]] (5 August 1914 – 5 June 1916)
* [[Edward Stanley, 17th Earl of Derby]] – Secretary of State for War (1916– )
* [[General (United Kingdom)|General]] [[Sir William Robertson, 1st Baronet|William Robertson]] – [[Chief of the General Staff (United Kingdom)|Chief of the Imperial General Staff]] (23 December 1915 – February 1918)
* General [[Sir Henry Wilson, 1st Baronet|Henry Wilson]] – Chief of the Imperial General Staff (February 1918 – February 1922)
* Field Marshal [[John French, 1st Earl of Ypres|John French]] – Commander-in-Chief of the [[British Expeditionary Force (World War I)|British Expeditionary Force]] (4 August 1914 – 15 December 1915)
* General/Field Marshal [[Douglas Haig, 1st Earl Haig|Douglas Haig]] – Commander-in-Chief of the British Expeditionary Force (15 December 1915 – 11 November 1918)
* General [[David Henderson (British Army officer)|Sir David Henderson]] – Director-General of Military Aeronautics
* General [[Hugh Trenchard, 1st Viscount Trenchard|Hugh Trenchard]] – Commander of the [[Royal Flying Corps]] – (August 1915 – January 1918) and [[Chief of the Air Staff (United Kingdom)|Chief of the Air Staff]] of the combined [[Royal Air Force]] – 1 April 1918 – 13 April 1918
* [[Brigadier (United Kingdom)#Historical rank of brigadier general|Brigadier General]] Sir [[Frederick Sykes]] – [[Chief of the Air Staff (United Kingdom)|Chief of the Air Staff]] – 13 April 1918 through 11 November 1918 (post-war to 31 March 1919)
* [[Winston Churchill]] – [[First Lord of the Admiralty]] – (1911 – May 1915)
* [[Arthur Balfour]]- First Lord of the Admiralty – (May 1915 – December 1916)
* [[Edward Carson]] – First Lord of the Admiralty – (10 December 1916 – 17 July 1917)
* [[Eric Geddes]] – First Lord of the Admiralty – (July 1917 – January 1919)
* [[Admiral of the Fleet (Royal Navy)|Admiral of the Fleet]] [[John Fisher, 1st Baron Fisher|John "Jackie" Fisher]] – [[First Sea Lord and Chief of the Naval Staff|First Sea Lord]] – (1914 – May 1915)
* [[Admiral (Royal Navy)|Admiral]] [[Henry Jackson (Royal Navy officer)|Henry Jackson]] – First Sea Lord – (May 1915 – November 1916)
* Admiral [[John Jellicoe, 1st Earl Jellicoe|John Jellicoe]] – Commander of the [[Grand Fleet]] (August 1914 – November 1916); First Sea Lord (November 1916 – December 1917)
* Admiral [[Rosslyn Wemyss, 1st Baron Wester Wemyss|Rosslyn Wemyss]] – First Sea Lord (December 1917 – November 1919)
* Admiral [[David Beatty, 1st Earl Beatty|David Beatty]] – Commander of the Grand Fleet (November 1916 – April 1919)
* General [[Archibald Murray]] – Commander of the [[Egyptian Expeditionary Force]] (January 1916 – June 1917)
* General [[Edmund Allenby, 1st Viscount Allenby|Edmund Allenby]] – Commander of the Egyptian Expeditionary Force (June 1917 – November 1918)
* [[Eric John Eagles Swayne]] – Commander of British forces in the [[Somaliland campaign|Somaliland Campaign]]
* [[William Peyton]] – commander and military secretary to the British Expeditionary Force
* [[Colonel (United Kingdom)|Colonel]] [[T. E. Lawrence]] –  a main leader of the [[Arab Revolt]]

====Dominion of Canada====
* [[Robert Borden]] – [[Prime Minister of Canada]] (1914–18)
* [[Sam Hughes]] – [[Minister of Militia and Defence]] (1914 – January 1915)
* [[Joseph Flavelle]] – Chairman of the [[Imperial Munitions Board]] (1915–19)
* {{flagicon|United Kingdom of Great Britain and Ireland|size=20px}} [[Lieutenant-general (United Kingdom)|Lieutenant-General]] [[Edwin Alderson]] – Commander of the unified [[Canadian Corps]] of the [[Canadian Expeditionary Force]] (26 January 1915 – September 1915)
* {{flagicon|United Kingdom of Great Britain and Ireland|size=20px}} [[General (United Kingdom)|General]] [[Julian Byng, 1st Viscount Byng of Vimy|Julian Byng]] – Commander of the unified Canadian Corps of the Canadian Expeditionary Force (June 1916 – June 1917)
* [[General (Canada)|General]] [[Arthur Currie]] – Commander of the unified Canadian Corps of the Canadian Expeditionary Force (June 1917 – August 1919)<ref>first Canadian to attain the rank of full [[general]]</ref>

====Commonwealth of Australia====
* [[Joseph Cook]] – [[Prime Minister of Australia]] (until 17 September 1914)
* [[Andrew Fisher]] – Prime Minister of Australia (17 September 1914 – 27 October 1915)
* [[Billy Hughes]] – Prime Minister of Australia (from 27 October 1915)
* {{flagicon|United Kingdom of Great Britain and Ireland|size=20px}} [[General (United Kingdom)|General]] [[William Birdwood]] – Commander of the [[Australian Corps]] (all five Australian infantry divisions serving on the Western Front) (November 1917 – May 1918)
* [[Lieutenant general (Australia)|Lieutenant General]] Sir [[John Monash]] – Commander of the [[Australian Corps]] (May 1918 –)
* [[Major general (Australia)|Major General]] [[William Holmes (Australian general)|William Holmes]] – Commander of the [[Australian Naval and Military Expeditionary Force]] (August 1914 – February 1915)
* Lieutenant General Sir [[Harry Chauvel]] – Commander of the [[Desert Mounted Corps]] (Sinai and Palestine) (August 1917 –)

====British India====
* [[Charles Hardinge, 1st Baron Hardinge of Penshurst]] – [[Governor-General of India|Viceroy of India]] (1910–1916)
* [[Frederic Thesiger, 1st Viscount Chelmsford]] – Viceroy of India (1916–1921)
* [[Robert Crewe-Milnes, 1st Marquess of Crewe]] – [[Secretary of State for India]] (May 1911 – May 1915)
* [[Austen Chamberlain]] – Secretary of State for India (May 1915 – July 1917)
* [[Edwin Montagu|Edwin Samuel Montagu]] – Secretary of State for India (July 1917 – March 1922)
* [[Beauchamp Duff]] – [[Commander-in-Chief, India|Commander-in-Chief]], India (March 1914 – October 1916)
* [[Sir Charles Monro, 1st Baronet|Charles Monro]] – Commander-in-Chief, India (October 1916 – November 1920)
* [[Lieutenant-general (United Kingdom)|Lieutenant-General]] [[John Nixon (Indian Army officer)|John Nixon]] – commander of the [[British Indian Army]] (active in the Middle East)

====Union of South Africa====
* [[General (United Kingdom)|General]] [[Louis Botha]] – [[Prime Minister of South Africa]]
* General [[Jan Smuts]] – led forces in the [[South West Africa campaign|South West Africa Campaign]] and [[East African campaign (World War I)|East African Campaign]], later a member of the [[Imperial War Cabinet]]

====Dominion of New Zealand====
* [[William Massey]] – [[Prime Minister of New Zealand]]
* General Sir [[Alexander Godley]] – Commandant of New Zealand Military Forces (to October 1914); Commander of the [[New Zealand Expeditionary Force]]s
* Major General Sir [[Alfred Robin|Alfred William Robin]] – Quartermaster-General and Commandant of New Zealand Military Forces (from October 1914)
* Major General Sir [[Andrew Hamilton Russell]] – Commander of the [[New Zealand Division]]

====Dominion of Newfoundland====
* [[Edward Morris, 1st Baron Morris|Sir Edward Morris]] – [[List of premiers of Newfoundland and Labrador|Prime Minister of Newfoundland]] (1909–1917)
* [[John Chalker Crosbie|Sir John Crosbie]] – Prime Minister of Newfoundland (1917–1918)
* [[William F. Lloyd|Sir William Lloyd]] – Prime Minister of Newfoundland (1918–1919)

===Japan===
* [[Emperor Taishō]] – [[Emperor of Japan]]
* [[Ōkuma Shigenobu]] – [[Prime Minister of Japan]] (16 April 1914 – 9 October 1916)
* [[Terauchi Masatake]] – Prime Minister of Japan (9 October 1916 – 29 September 1918)
* [[Hara Takashi]] – Prime Minister of Japan (29 September 1918 – 4 November 1921)
* [[Katō Sadakichi]] – Commander-in-Chief of the [[2nd Fleet (Imperial Japanese Navy)|Second Fleet]] deployed to the [[Siege of Tsingtao]]
* [[Kōzō Satō]] – Commander of the Second Special Task Fleet
* [[Kamio Mitsuomi]] – Commander of Allied land forces [[Siege of Tsingtao|at Tsingtao]]

===Italy (1915–1918)===
* [[Victor Emmanuel III of Italy|Victor Emmanuel III]] – [[King of Italy]]
* [[Antonio Salandra]] – [[Prime Minister of Italy|Prime Minister]] (until 18 June 1916)
* [[Paolo Boselli]] – Prime Minister (18 June 1916 – 29 October 1917)
* [[Vittorio Emanuele Orlando]] – Prime Minister (from 29 October 1917)
* [[Luigi Cadorna]] – Commander-in-Chief of the [[Royal Italian Army]]
* [[Armando Diaz]] – Chief of General Staff of the Royal Italian Army
* [[Prince Luigi Amedeo, Duke of the Abruzzi|Luigi, Duke of Abruzzi]] – Commander-in-Chief of the Adriatic Fleet of Italy (1914–17)
* [[Paolo Thaon di Revel]] – Admiral of the [[Regia Marina|Royal Italian Navy]]

===Romania (1916–1918)===
* [[Ferdinand I of Romania|Ferdinand I]] – [[King of Romania]]
* General [[Constantin Prezan]] – Chief of the General Staff of Romania
* [[Ion I. C. Brătianu]] – Prime Minister of Romania
* [[Vintilă Brătianu]] – Secretary of War
* [[Mareșal (Romania)|Field Marshal]] [[Alexandru Averescu]] – Commander of the [[Second Army (Romania)|2nd Army]], 3rd Army, then Army Group South
* General [[Eremia Grigorescu]] – Commander of the [[1st Infantry Division (Romania)|1st Army]]

===Portugal (1916–1918)===
* [[Bernardino Machado]] – [[President of Portugal]] (until 12 December 1917)
* [[Afonso Costa]] – [[Prime Minister of Portugal]] (until 15 March 1916; then again 25 April 1917 – 10 December 1917)
* [[António José de Almeida]] – Prime Minister of Portugal (15 March 1916 – 25 April 1917)
* [[Sidónio Pais]] – Prime Minister of Portugal and War Minister (11 December 1917 – 9 May 1918) and President of Portugal (from 9 May 1918)
* [[José Norton de Matos]] – War Minister (until 10 December 1917)
* [[João Tamagnini Barbosa]] – Interim War Minister (9 May 1918 – 15 May 1918)
* Amílcar Mota – Secretary of State for War (15 May 1918 – 8 October 1918)
* Álvaro de Mendonça – Secretary of State for War (from 8 October 1918)
* [[Fernando Tamagnini de Abreu e Silva|Fernando Tamagnini de Abreu]] – Commander of the [[Portuguese Expeditionary Corps|Portuguese Expeditionary Corps (CEP)]]
* [[José Augusto Alves Roçadas]] – Commander of the Portuguese Forces in Southern Angola
* José Luís de Moura Mendes – Commander of the Portuguese Forces in Eastern Africa (until June 1916)
* [[José César Ferreira Gil]] – Commander of the Portuguese Forces in Eastern Africa (from June 1916)
* Sousa Rosa – Commander of the Portuguese Forces in Eastern Africa (from 1917)

===Greece (1916/17–1918)===
[[File:Greece-1917-war-poster-02-petros roumbos-56x83cm.jpg|thumb|upright|Greek propaganda poster]]
* [[Constantine I of Greece|Constantine I]]: King of Greece, he retired from the throne in June 1917, due to Allied pressure, without formally abdicating.
* [[Alexander of Greece|Alexander]]: King of Greece from 1917 after his father was forced into exile
* [[Eleftherios Venizelos]]: Prime Minister of Greece after 13 June 1917
* [[Panagiotis Danglis]]: Greek general of the Hellenic Army

===United States (1916–1918)===
[[File:World War I US Army Air Service Recruiting Poster1.jpg|thumb|upright|USAAS recruiting poster, 1918]]
* [[Woodrow Wilson]] – [[President of the United States]]/Commander-In-Chief of the US Armed Forces
* [[Newton D. Baker]] – [[United States Secretary of War|US Secretary of War]]
* [[Josephus Daniels]] – [[United States Secretary of the Navy|US Secretary of the Navy]]
* [[Major general (United States)|Major General]]/[[General (United States)|General]] [[John J. Pershing]] – Commander of the [[American Expeditionary Forces]]
* [[Rear admiral (United States)|Rear Admiral]]/[[Vice admiral (United States)|Vice Admiral]] [[William Sims]] – Commander of [[United States Navy|US Naval Forces in European Waters]]
* [[Brigadier general (United States)|Brigadier General]] [[Mason Patrick]] – Commander of the [[United States Army Air Service|US Army Air Service]]

===Siam (1917–1918)===
{{Main|Rattanakosin Kingdom (1782–1932)|Siam in World War I}}
[[File:Siamese Troops (Thai) Arc de Triomphe WW1 1919.jpg|thumb|Troops of the [[Siamese Expeditionary Forces]] marching in Paris, 1919]]
* [[Vajiravudh]], [[King of Siam]]
* [[Chaophraya Bodindechanuchit (Arun Chatrakul)|Chaophraya Bodindechanuchit]], [[Ministry of Defence (Thailand)|Minister of Defence]]
* [[Chakrabongse Bhuvanath]], Supreme Commander of the Siamese Expeditionary Forces in [[World War I]]
* [[Phraya Thephatsadin]], Commander of the [[Siamese Expeditionary Forces]] in the [[Western Front (World War I)|Western Front]]

===Brazil (1917–1918)===
{{Main|Brazil during World War I}}
[[File:GLAM MB Cruzador-Auxiliar (45024099444).jpg|thumb|The Brazilian ship Cruzador ''Bahia'']]
* [[Venceslau Brás]] – [[President of Brazil]]
* [[Pedro Max Fernando Frontin|Pedro Frontin]], Chief of the ''Divisão Naval em Operações de Guerra'' (Naval Division in War Operations)
* [[José Pessoa Cavalcanti de Albuquerque]], lieutenant of the Brazilian Army in France
* Napoleão Felipe Aché, Chief of Brazilian Military Mission in France (1918–1919)
* [[Doctor of Medicine|M.D.]] Nabuco Gouveia – Chief of Brazilian Military Medical Commission

===Armenia (1917–1918)===
* [[Hovhannes Kajaznuni]] – first [[Prime Minister of Armenia|Prime Minister]] of the [[First Republic of Armenia]]
* [[Andranik|General Andranik]] – military commander and statesman of the [[Caucasus campaign|Caucasus Campaign]]
* [[Aram Manukian]] – Minister of Internal Affairs of the First Republic of Armenia
* [[Drastamat Kanayan]] – military commander and member of the [[Armenian Revolutionary Federation]]
* [[Tovmas Nazarbekian]] – Commander-in-Chief of the First Republic of Armenia
* [[Movses Silikyan]] – army general and national hero

===Czechoslovakia (1918)===
* [[Tomáš Masaryk|Tomáš Garrigue Masaryk]] – first [[List of presidents of Czechoslovakia|President]] of [[First Czechoslovak Republic|Czechoslovakia]]
* [[Milan Rastislav Štefánik]] – Commander of the [[Czechoslovak Legion]]
* [[Edvard Beneš]] – [[Ministry of Foreign Affairs (Czechoslovakia)|Minister of Foreign Affairs]] and [[Ministry of the Interior (Czechoslovakia)|the Interior]]

==Personnel and casualties==
{{See also|World War I casualties}}
[[File:WorldWarI-MilitaryDeaths-EntentePowers-Piechart.svg|thumb|A pie-chart showing the military deaths of the Allied Powers]]
These are estimates of the cumulative number of different personnel in uniform 1914–1918, including army, navy and auxiliary forces. At any one time, the various forces were much smaller. Only a fraction of them were frontline combat troops. The numbers do not reflect the length of time each country was involved.

<!--Please do not change any numbers until a reference is provided or has been suggested/discussed on the talk page.-->
{| class="wikitable sortable plainrowheaders" style="text-align: right;"
|+ World War I personnel and casualties, by country
|-
! scope="col" style="width:20%;" | Allied power
! scope="col" style="width:20%;" | Mobilized personnel
! scope="col" style="width:20%;" | Military fatalities
! scope="col" style="width:20%;" | Wounded in action
! scope="col" style="width:20%;" | Casualties, total
! scope="col" style="width:20%;" | Casualties, % of total mobilised
|-
! scope="row" | Australia
|412,953{{sfn|War Office Statistics|2006|p=756}}||61,928 (14.99%){{efn|Australia casualties<br>Included in total are 55,000 killed or missing in action and died of wounds{{sfn|Urlanis|2003|p=85}}-.<br>The [[Commonwealth War Graves Commission]] Annual Report 2005–2006 is the source of total military dead.{{sfn|CWGC|2006}}–<br>Totals include 2,005 military deaths during 1919–21{{sfn|CWGC|2012}}–. The 1922 [[War Office]] report listed 59,330 Army war dead.{{sfn|War Office Statistics|2006|p=237}}}} ||152,171||214,099||52% <!--Please do not change casualty numbers without discussion-->
|-
! scope="row" | Belgium
|267,000<ref name =Tucker172/>||38,172 (14.29%){{efn|Belgium casualties<br>Included in total are 35,000 killed or missing in action and died of wounds{{sfn|Urlanis|2003|p=85}} Figures include 13,716 killed and 24,456 missing up until Nov.11, 1918. "These figures are approximate only, the records being incomplete." .{{sfn|War Office Statistics|2006|p=352}}}} ||44,686||82,858||31% <!--Please do not change casualty numbers without discussion-->
|-
! scope="row" | Brazil
|1,713{{sfn|Donato|1987|p=}}{{Page needed|date=September 2022}}||100 (5.84%)<ref>Francisco Verras; "D.N.O.G.: contribuicao da Marinha Brasileira na Grande Guerra" ("DNOG; the role of Brazilian Navy in the Great War") {{in lang|pt}} "A Noite" Ed. 1920</ref>||0||100||5.84%<!--Please do not change casualty numbers without discussion-->
|-
! scope="row" | Canada
|628,964{{sfn|War Office Statistics|2006|p=756}}||64,944 (10.32%){{efn|Canada casualties<br>Included in total are 53,000 killed or missing in action and died of wounds.{{sfn|Urlanis|2003|p=85}}<br>The [[Commonwealth War Graves Commission]] Annual Report 2005–2006 is the source of total military dead.{{sfn|CWGC|2006}}<br>Totals include 3,789 military deaths during 1919–21 and 150 [[Merchant Navy]] deaths{{sfn|CWGC|2012}}–. The losses of Newfoundland are listed separately on this table. The 1922 [[War Office]] report listed 56,639 Army war dead.{{sfn|War Office Statistics|2006|p=237}}}}||149,732||214,676||34% <!--Please do not change casualty numbers without discussion-->
|-
! scope="row" | France
|8,410,000<ref name =Tucker172/>||1,397,800 (16.62%){{efn|France casualties<br>Included in total are 1,186,000 killed or missing in action and died of wounds.{{sfn|Urlanis|2003|p=85}} Totals include the deaths of 71,100 French colonial troops.{{Sfn|Huber|1931|p=414}}-Figures include war related military deaths of 28,600 from 11/11/1918 to 6/1/1919.{{sfn|Huber|1931|p=414}} }} ||4,266,000||5,663,800||67% <!--Please do not change casualty numbers without discussion-->
|-
! scope="row" | Greece
|230,000<ref name =Tucker172/>||26,000 (11.30%){{efn|Greece casualties<br>Jean Bujac in a campaign history of the Greek Army in World War One listed 8,365 combat related deaths and 3,255 missing,{{sfn|Bujac|1930|p=339}} The Soviet researcher Boris Urlanis estimated total dead of 26,000 including 15,000 military deaths due disease{{sfn|Urlanis|2003|p=160}} }} ||21,000||47,000||20% <!--Please do not change casualty numbers without discussion-->
|-
! scope="row" | India
|1,440,437{{sfn|War Office Statistics|2006|p=756}}||74,187 (5.15%){{efn|India casualties<br>British India included present-day India, [[Pakistan]] and [[Bangladesh]].<br>Included in total are 27,000 killed or missing in action and died of wounds.{{sfn|Urlanis|2003|p=85}}<br>The [[Commonwealth War Graves Commission]] Annual Report 2005–2006 is the source of total military dead.{{sfn|CWGC|2006}}<br>Totals include 15,069 military deaths during 1919–21 and 1,841 [[Canadian Merchant Navy]] dead.{{sfn|CWGC|2012}} The 1922 [[War Office]] report listed 64,454 Army war dead{{sfn|War Office Statistics|2006|p=237}} }} ||69,214||143,401||10% <!--Please do not change casualty numbers without discussion-->
|-
! scope="row" | Italy
|5,615,000<ref name =Tucker172/>||651,010 (11.59%){{efn|Italy casualties<br>Included in total are 433,000 killed or missing in action and died of wounds{{sfn|Urlanis|2003|p=85}}<br>Figures of total military dead are from a 1925 Italian report using official data.{{sfn|Mortara|1925 |p=}}{{Page needed|date=September 2022}}}} ||953,886||1,604,896||29% <!--Please do not change casualty numbers without discussion-->
|-
! scope="row" | Japan
|800,000<ref name =Tucker172/>||415 (0.05%){{efn|War dead figure is from a 1991 history of the Japanese Army.{{sfn|Harries|Harries|1991|p=111}} }} ||907||1,322||<1% <!--Please do not change casualty numbers without discussion-->
|-
! scope="row" | Monaco
|80<ref name=autogenerated1>{{cite web|url=http://www.nicematin.com/article/societe/monaco-11-novembre-ces-monegasques-morts-au-champ-dhonneur.40790.html|title=Monaco 11-Novembre : ces Monégasques morts au champ d'honneur|access-date=31 December 2012|archive-url=https://web.archive.org/web/20150402101253/http://www.nicematin.com/article/societe/monaco-11-novembre-ces-monegasques-morts-au-champ-dhonneur.40790.html|archive-date=2 April 2015|url-status=live}}</ref>||8 (10.00%)<ref name=autogenerated1 />||0||8<ref name=autogenerated1 />||10%
|-
! scope="row" | Montenegro
|50,000<ref name =Tucker172/>||3,000 (6.00%)||10,000||13,000||26% <!--Please do not change casualty numbers without discussion-->
|-
! scope="row" | Nepal
|200,000<ref>Jain, G (1954) India Meets China in Nepal, Asia Publishing House, Bombay P92</ref>||30,670 (15.33%)||21,009||49,823||25%<!--Please do not change casualty numbers without discussion-->
|-
! scope="row" | New Zealand
|128,525{{sfn|War Office Statistics|2006|p=756}}||18,050 (14.04%){{efn|New Zealand casualties<br>Included in total are 14,000 killed or missing in action and died of wounds.{{sfn|Urlanis|2003|p=85}}<br>The [[Commonwealth War Graves Commission]] Annual Report 2005–2006 is the source of total military dead.{{sfn|CWGC|2006}}<br>Totals include 702 military deaths during 1919–21.{{sfn|CWGC|2012}} The 1922 [[War Office]] report listed 16,711 Army war dead.{{sfn|War Office Statistics|2006|p=237}}}} ||41,317||59,367||46% <!--Please do not change casualty numbers without discussion-->
|-
! scope="row" | Portugal
|100,000<ref name =Tucker172/>||7,222 (7.22%){{efn|Portugal casualties<br>Figures include the following killed and died of other causes up until Jan.1, 1920; 1,689 in France and 5,332 in Africa. Figures do not include an additional 12,318 listed as missing and [[POW]].{{sfn|War Office Statistics|2006|p=354}}}} ||13,751||20,973||21% <!--Please do not change casualty numbers without discussion-->
|-
! scope="row" | Romania
|750,000<ref name =Tucker172/>||250,000 (33.33%){{efn|Romania casualties<br>Military dead is "The figure reported by the Rumanian Government in reply to a questionnaire from the International Labour Office".{{sfn|Urlanis|2003|p=64}} Included in total are 177,000 killed or missing in action and died of wounds.{{sfn|Urlanis|2003|p=85}}}} ||120,000||370,000||49% <!--Please do not change casualty numbers without discussion-->
|-
! scope="row" | Russia
|12,000,000<ref name =Tucker172/>||1,811,000 (15.09%){{efn|Russia casualties<br>Included in total are 1,451,000 killed or missing in action and died of wounds.{{sfn|Urlanis|2003|p=85}} The estimate of total Russian military losses was made by the Soviet researcher Boris Urlanis.{{sfn|Urlanis|2003|p=46–57}} }} ||4,950,000 ||6,761,000||56% <!--Please do not change casualty numbers without discussion-->
|-
! scope="row" | Serbia
|707,343<ref name =Tucker172/>||275,000 (38.87%){{efn|Serbia casualties<br>Included in total are 165,000 killed or missing in action and died of wounds.{{sfn|Urlanis|2003|p=85}} The estimate of total combined Serbian and Montenegrin military losses of 278,000 was made by the Soviet researcher Boris Urlanis{{sfn|Urlanis|2003|p=62–64}} }} ||133,148||408,148||58%<!--Please do not change casualty numbers without discussion-->
|-
! scope="row" | Siam
|1,284<ref name=Gilbert94/>{{Page needed|date=September 2021}}||19 (1.48%)||0||19||2%<!--Please do not change casualty numbers without discussion-->
|-
! scope="row" | South Africa
| 136,070{{sfn|War Office Statistics|2006|p=756}}||9,463 (6.95%){{efn|South Africa casualties<br>Included in total are 5,000 killed or missing in action and died of wounds{{sfn|Urlanis|2003|p=85}}<br>The [[Commonwealth War Graves Commission]] Annual Report 2005–2006 is the source of total military dead.{{sfn|CWGC|2006}}<br>Totals include 380 military deaths during 1919–21{{ref|CWGC|15}}. The 1922 [[War Office]] report listed 7,121 Army war dead.{{sfn|War Office Statistics|2006|p=237}}}} ||12,029||21,492||16% <!--Please do not change casualty numbers without discussion-->
|-
! scope="row" | United Kingdom
|6,211,922<ref name =Gilbert94/>||886,342 (14.26%){{efn|UK and [[Crown Colonies]] casualties<br>Included in total are 624,000 killed or missing in action and died of wounds.{{sfn|Urlanis|2003|p=85}}<br>The [[Commonwealth War Graves Commission]] Annual Report 2005–2006 is the source of total military dead.{{sfn|CWGC|2006}}<br>Military dead total includes 34,663 deaths during 1919–21 and 13,632 [[British Merchant Navy]] deaths.{{sfn|CWGC|2012}} The 1922 [[War Office]] report listed 702,410 war dead for the UK,{{sfn|War Office Statistics|2006|p=237}} 507 from "Other colonies"{{sfn|War Office Statistics|2006|p=237}} and the [[Royal Navy]] (32,287).{{sfn|War Office Statistics|2006|p=339}}<br>The [[British Merchant Navy]] losses of 14,661 were listed separately;{{sfn|War Office Statistics|2006|p=339}} The 1922 [[War Office]] report detailed the deaths of 310 military personnel due to air and sea bombardment of the UK.{{sfn|War Office Statistics|2006|p=674–678}}}} ||1,665,749||2,552,091||41% <!--Please do not change casualty numbers without discussion-->
|-
! scope="row" | United States
|4,355,000<ref name =Tucker172/>||53,402 (1.23%){{efn|United States casualties<br>Official military war deaths listed by the US Dept. of Defense for the period ending 31 Dec 1918 are 116,516; which includes 53,402 battle deaths and 63,114 other deaths. {{Cite web |title=Principal Wars in Which the United States Participated U.S. Military Personnel Serving and Casualties a/ |url=http://siadapp.dior.whs.mil/personnel/CASUALTY/WCPRINCIPAL.pdf |url-status=dead |archive-url=https://web.archive.org/web/20070125063136/http://siadapp.dior.whs.mil/personnel/CASUALTY/WCPRINCIPAL.pdf |archive-date=Jan 25, 2007 |publisher=Department of Defense Statistical Information Analysis Division}} The US Coast Guard lost an additional 192 dead .{{sfn|Clodfelter|2002|p=481}}}}||205,690||259,092||5.9% <!--Please do not change casualty numbers without discussion-->
|- class="sortbottom"
! scope="row" style="font-weight: bold;" | Total
! scope="col" style="text-align: right;" | 42,244,409
! scope="col" style="text-align: right;" | 5,741,389
! scope="col" style="text-align: right;" | 12,925,833
! scope="col" style="text-align: right;" | 18,744,547
! scope="col" style="text-align: right;" | 49% <!--Please do not change casualty numbers without discussion-->
|}

==See also==
* [[Allied intervention in the Russian Civil War]]
* [[Causes of World War I]]
* [[Color books]], transcripts of official documents released by each nation early in the war
* [[Diplomatic history of World War I]]
** [[British entry into World War I]]
** [[French entry into World War I]]
* [[Historiography of the causes of World War I]]
* [[Home front during World War I]]
** [[Belgium in World War I]]
** [[French Third Republic#First World War|France in World War I]]
** [[History of Germany during World War I|Germany in World War I]]
** [[Military history of Italy during World War I|Italy in World War I]]
** [[Romania during World War I|Romania in World War I]]
** [[History of the United Kingdom during World War I|United Kingdom in World War I]]
** [[United States home front during World War I|United States in World War I]]
** [[Japan during World War I|Japan in World War I]]
* [[International relations of the Great Powers (1814–1919)]]
* [[July Crisis]]

==Footnotes==
{{notelist}}

==References==
{{reflist}}

==Bibliography==
{{Further|List of World War I books}}
* Ellis, John and Mike Cox. ''The World War I Databook: The Essential Facts and Figures for All the Combatants'' (2002)
* Esposito, Vincent J. ''The West Point Atlas of American Wars: 1900–1918'' (1997); despite the title covers entire war; [https://web.archive.org/web/20070102173709/http://www.dean.usma.edu/HISTORY/web03/atlases/great%20war/great%20war%20index.htm online maps from this atlas]
* Falls, Cyril. ''The Great War'' (1960), general military history
* {{cite book | last=Gilbert | first=Martin | title=First World War | publisher=HarperCollins | year=1995 | isbn=978-0006376668 | oclc=1244719073 | url=https://archive.org/details/firstworldwar0000gilb_a3d4 }}
* Gooch, G. P. ''Recent Revelations of European Diplomacy'' (1940), 475pp; summarises memoirs of major participants
* Higham, Robin and Dennis E. Showalter, eds. ''Researching World War I: A Handbook'' (2003); historiography, stressing military themes
* Pope, Stephen and Wheal, Elizabeth-Anne, eds. ''The Macmillan Dictionary of the First World War'' (1995)
* Strachan, Hew. ''The First World War: Volume I: To Arms'' (2004)
* Trask, David F. ''The United States in the Supreme War Council: American War Aims and Inter-Allied Strategy, 1917–1918'' (1961)
* {{cite book |author=Tucker Spencer C |title=The European Powers in the First World War: An Encyclopedia |publisher=Garland |place=New York |year=1999 |isbn=978-0-8153-3351-7 }}
* Tucker, Spencer, ed. ''The Encyclopedia of World War I: A Political, Social, and Military History'' (5 volumes) (2005); online at eBook.com
* United States. War Dept. General Staff. ''Strength and organisation of the armies of France, Germany, Austria, Russia, England, Italy, Mexico and Japan (showing conditions in July, 1914)'' (1916) [https://archive.org/details/strengthorganiza00unit online]
* {{cite book |title=Statistics of the Military Effort of the British Empire During the Great War 1914–1920 |author=The War Office |place=Uckfield, East Sussex |orig-year=1922 |year=2006 |publisher=Military and Naval Press |isbn=978-1-84734-681-0 |oclc=137236769 |ref={{sfnref|War Office Statistics|2006}}}}
* {{citation |author-link=Commonwealth War Graves Commission |author=CWGC |date=2006 |title=Annual Report 2005–2006 |url=http://www.cwgc.org/admin/files/6%20Statistics.pdf |access-date=28 January 2007 |archive-date=16 June 2007 |archive-url=https://web.archive.org/web/20070616100700/http://www.cwgc.org/admin/files/6%20Statistics.pdf |url-status=dead }}
* {{citation |author-link=Commonwealth War Graves Commission |author=CWGC|title=Debt of Honour Register |url=http://www.cwgc.org/debt_of_honour.asp?menuid=14 |url-status=dead |archive-url=https://web.archive.org/web/20120118052753/http://www.cwgc.org/debt_of_honour.asp?menuid=14 |archive-date=18 January 2012 |date=2012 }}
* {{cite book |last=Urlanis |first=Boris |title=Wars and Population |orig-year=1971, Moscow |oclc=123124938 |year=2003 |place=Honolulu |publisher=University Press of the Pacific }}
* {{cite book|last=Huber |first=Michel |title=La population de la France pendant la guerre, avec un appendice sur Les revenus avant et après la guerre |place=Paris |year=1931 |language=fr |oclc=4226464 }}
* {{cite book |last=Bujac |first=Jean Léopold Emile |title=Les campagnes de l'armèe Hellènique 1918–1922 |place=Paris |publisher=Charles-Lavauzelle |year=1930 |language=fr |oclc=10808602 }}
* {{cite book |last=Mortara |first=Giorgio |title=La Salute pubblica in Italia durante e dopo la Guerra |place=New Haven, Connecticut |publisher=Yale University Press |year=1925 |language=it |oclc=2099099 }}
* {{cite book |last1=Harries |first1=Merion |last2= Harries |first2= Susie |title=Soldiers of the Sun: The Rise and Fall of the Imperial Japanese Army |publisher=Random House |year=1991 |isbn=978-0-679-75303-2 |oclc=32615324 }}
* {{cite book |last=Clodfelter |first=Micheal |title=Warfare and Armed Conflicts: A Statistical Reference to Casualty and Other Figures, 1500–2000 |edition=2nd |year=2002 |location=London |publisher=McFarland |isbn=978-0-7864-1204-4 |oclc=48066096 }}
* {{cite book |first=Hernâni |last=Donato |title=Dicionário das Batalhas Brasileiras |year=1987 |location=Rio de Janeiro |publisher=IBRASA |isbn=978-85-348-0034-1 }}

{{World War 1}}
{{WWI history by nation}}
{{authority control}}

{{DEFAULTSORT:Allies of World War I}}
[[Category:Allies of World War I]]
[[Category:1919 in law]]
[[Category:20th-century military alliances]]
[[Category:Aftermath of World War I]]
[[Category:Military alliances involving Australia]]
[[Category:Military alliances involving Canada]]
[[Category:Military alliances involving France]]
[[Category:Military alliances involving New Zealand]]
[[Category:Military alliances involving South Africa]]
[[Category:Military alliances involving the United Kingdom]]
[[Category:Military alliances involving the United States]]
[[Category:World War I by country]]
[[Category:History of diplomacy]]