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{{short description|Prevention of trade or movement by force}}
{{Other uses|Blockade (disambiguation)}}
{{more citations needed|date=May 2022}}
{{Use dmy dates|date=April 2019}}
[[File:Scott-anaconda.jpg|thumb|upright=1.3|''[[Winfield Scott|Scott's]] great snake'', a cartoon map illustrating the [[Union (American Civil War)|Union]] blockade of the [[Confederate States of America|Confederacy]] during the [[American Civil War]], known as the [[Anaconda Plan]], illustrated by J.B. Elliott]]
[[File:C-47s at Tempelhof Airport Berlin 1948.jpg|thumb|[[Douglas C-47 Skytrain|C47]]s unloading at [[Tempelhof Airport]] in [[Berlin]], part of the airlift of supplies which broke the [[Soviet Union]]'s 1948 [[Berlin Blockade|land blockade of West Berlin]]]]
{{war}}

A '''blockade''' is the act of actively preventing a country or region from receiving or sending out [[food]], [[Contraband|supplies]], [[Materiel|weapons]], or [[communication]]s, and sometimes people, by [[military force]].
A blockade differs from an [[embargo]] or [[International sanctions|sanction]], which are legal barriers to trade rather than physical barriers. It is also distinct from a [[siege]] in that a blockade is usually directed at an entire country or region, rather than a fortress or city and the objective may not always be to conquer the area.

A blockading power can seek to cut off all maritime transport from and to the blockaded country, although stopping all land transport to and from an area may also be considered a blockade. Blockades restrict the trading rights of neutrals, who must submit for inspection for contraband, which the blockading power may define narrowly or broadly, sometimes including food and medicine. In the 20th century, [[air power]] has also been used to enhance the effectiveness of blockades by halting air traffic within the blockaded airspace.

Close patrol of hostile ports, in order to prevent naval forces from putting to sea, is also referred to as a blockade. When coastal cities or fortresses were besieged from the landward side, the besiegers would often blockade the seaward side as well. Most recently, blockades have sometimes included cutting off electronic communications by [[radio jamming|jamming radio]] signals and severing [[Submarine communications cable|undersea cables]]. Blockades often result in the starvation of the civilian population, notably during the [[Blockade of Germany (1914–1919)|blockade of Germany]] during [[World War I]] and the [[blockade of Biafra]] during the [[Nigerian Civil War]].<ref>{{cite book |last1=Nicholas Mulder, [[Boyd van Dijk]] |title=Contingency in International Law: On the Possibility of Different Legal Histories |date=2021 |publisher=Oxford University Press |pages=370– |language=en |chapter=Why Did Starvation Not Become the Paradigmatic War Crime in International Law?}}</ref>

According to modern international law, blockades are an act of war.<ref name=":0">{{cite journal |last1=Russell |first1=Alison Lawlor |title=Digital Blockade or Corporate Boycott?: A New Tactic of War |journal=Æther: A Journal of Strategic Airpower & Spacepower |date=2023 |volume=2 |issue=1 |pages=16–30 |jstor=48714684 |url=https://www.jstor.org/stable/48714684 |issn=2771-6120}}</ref> In that sense, a blockade can be legal only if applied in [[self-defense]] – but never as part of a [[war of aggression]]. Blockades are illegal when used as to starve or to collectively punish a civilian population.<ref name=":1">{{cite news |last1=Dannenbaum |first1=Tom |title=What You Need to Know: International Humanitarian Law and Russia's Termination of the Black Sea Grain Initiative |url=https://www.justsecurity.org/87414/what-you-need-to-know-ihl-and-russias-termination-of-the-black-sea-grain-initiative/ |access-date=1 November 2023 |work=Just Security |date=28 July 2023}}</ref><ref name=":2">{{cite journal |last1=Dannenbaum |first1=Tom |title=Siege Starvation: A War Crime of Societal Torture |journal=Chicago Journal of International Law |date=2021–2022 |volume=22 |pages=368 |url=https://heinonline.org/HOL/LandingPage?handle=hein.journals/cjil22&div=25&id=&page=}}</ref><ref name=":3">{{cite web |title=Unlawful Blockades as Crimes Against Humanity {{!}} ASIL |url=https://www.asil.org/insights/volume/22/issue/5/unlawful-blockades-crimes-against-humanity |website=www.asil.org |language=en}}</ref><ref name=":4">{{cite web |title=Rule 53. Starvation as a Method of Warfare |url=https://ihl-databases.icrc.org/en/customary-ihl/v1/rule53 |website=ihl-databases.icrc.org |access-date=1 November 2023}}</ref><ref name=":5">{{Cite web |title=Report of the Secretary-General’s Panel of Inquiry on the 31 May 2010 Flotilla Incident |url=https://graphics8.nytimes.com/packages/pdf/world/Palmer-Committee-Final-report.pdf}}</ref> In such case, they are a [[war crime]] and potentially a [[crime against humanity]].<ref>{{cite journal |last1=Dannenbaum |first1=Tom |date=2021–2022 |title=Siege Starvation: A War Crime of Societal Torture |url=https://heinonline.org/HOL/LandingPage?handle=hein.journals/cjil22&div=25&id=&page= |journal=Chicago Journal of International Law |volume=22 |pages=368}}</ref><ref>{{cite web |title=Unlawful Blockades as Crimes Against Humanity {{!}} ASIL |url=https://www.asil.org/insights/volume/22/issue/5/unlawful-blockades-crimes-against-humanity |website=www.asil.org |language=en}}</ref>

==History==
Although primitive naval blockades have been in use for millennia, early attempts were limited by the time ships were able to stay at sea uninterruptedly.<ref>{{Cite book |last =Pitassi |first =Michael |title =The Roman navy: ships, men & warfare, 350 BC - AD 475 |date =2012 |publisher =Seaforth Publ |isbn =978-1-84832-090-1 |location =Barnsley |chapter =Chapter 7, Operations: Blockades}}</ref> The first successful attempts at establishing a full naval blockade were made by the British [[Royal Navy]] during the [[Seven Years' War]] (1754–1763) against [[France]].<ref>{{cite book |url=https://books.google.com/books?isbn=0203029496 |title=Seapower and Naval Warfare, 1650–1830 |author=Richard Harding |year=2002 |publisher=Routledge |access-date=7 February 2013}}</ref> Following [[Battle of Quiberon Bay|the 1759 British naval victory at Quiberon Bay]], which ended any immediate threat of a major [[Planned French invasion of Britain (1759)|invasion of Britain]],<ref>Anderson p.381-83</ref> the British Royal Navy established a [[Great Britain in the Seven Years' War | close blockade on the French coast]]. This starved French ports of commerce, weakening France's economy. [[Edward Hawke, 1st Baron Hawke|Admiral Edward Hawke]] took command of the blockading fleet off [[Brest, France|Brest]] and extended the blockade to cover the entire French Atlantic coast from [[Dunkirk]] to [[Bordeaux]], and also to [[Marseille]] on France's Mediterranean coast.<ref>Corbett p.86</ref>
During the [[French and Indian War | North American operations of the Seven Years' War]], the British Royal Navy also blockaded the French on the other side of the Atlantic, specifically impeding access and supply to the colonies of [[New France]] on the [[St. Lawrence River | St. Lawrence]].<ref>
{{cite book
 |last1                = Proulx
 |first1               = Gilles
 |author-link1         = Gilles Proulx
 |date                 = 1 January 1984
 |chapter              = The Atlantic Course
 |title                = Between France and New France: Life Aboard the Tall Sailing Ships
 |url                  = https://books.google.com/books?id=c9fvlKja1IEC
 |publication-place    = Toronto
 |publisher            = Dundurn
 |page                 = 51
 |isbn                 = 9781770700499
 |access-date          = 22 March 2025
 |quote                = The route through the [[Strait of Belle Isle]] was actually the result of international politics: the English blockade of New France forced the French to slip though this passage.
}}
</ref> Blockades thus contributed to the [[Conquest of New France |French loss of Canada]] in 1763.<ref>
{{cite book
 |last1                = Nester
 |first1               = William R.
 |date                 = 7 May 2014
 |chapter              = The French Empire
 |title                = The French and Indian War and the Conquest of New France
 |url                  = https://books.google.com/books?id=l_mJAwAAQBAJ
 |publication-place    = Norman
 |publisher            = University of Oklahoma Press
 |page                 = 89
 |isbn                 = 9780806145730
 |access-date          = 22 March 2025
 |quote                = During the French and Indian War, with Canada's population swollen by several thousand more unproductive mouths to feed, starvation stalked the colony if the supply fleet did not arrive by late spring. For the war's last three years, stomach-pinched Canadians spent months vainly scanning the Saint Lawrence before a few ships finally appeared that managed to evade the British blockade.
}}
</ref>

The strategic importance of blockade became increasingly apparent during the [[French Revolutionary Wars]] of 1792 to 1802 and in [[Napoleonic Wars]] of 1803 to 1815, when the Royal Navy successfully blockaded France, leading to major economic disruptions. The [[Union blockade]] of southern ports was a major factor in the [[American Civil War]] of 1861 to 1865. During [[World War I]] (1914-1918), [[Allies of World War I|the Allies]] [[Blockade of Germany (1914–1919) | blockaded the Central Powers]], depriving them of food-supplies and strategic materials. [[U-boat Campaign (World War I)|Germany's attempted U-boat blockade of Britain]] caused some shortages, but ultimately failed. A similar outcome followed in [[World War II]] (1939-1945).

Naval strategic thinkers, such as Sir [[Julian Corbett]] (1854-1922) and [[Alfred Thayer Mahan]] (1840-1914), wrote that naval conflicts were won primarily by decisive battles, but also by blockade.<ref>{{cite web |url =https://www.usnwc.edu/getattachment/85c80b3a-5665-42cd-9b1e-72c40d6d3153/NWC-1005-NAVAL-CLASSICAL-THINKERS-AND-OPERATIONAL-.aspx |title =Naval Classical Thinkers and Operational Art |year =2009 |first1 =Dr. Milan |last1 =Vego |publisher =[[Naval War College]] |pages =4; 8 |access-date = 22 March 2025 |url-status =dead |archive-url =https://web.archive.org/web/20170131144505/https://www.usnwc.edu/getattachment/85c80b3a-5665-42cd-9b1e-72c40d6d3153/NWC-1005-NAVAL-CLASSICAL-THINKERS-AND-OPERATIONAL-.aspx |archive-date =31 January 2017 | quote = Based on his study of naval history, Mahan contemplated two main methods in obtaining and maintaining command of the sea: decisive battle and blockade. [...] Corbett believed that the principal methods for securing control of the sea are by obtaining a decision and by conducting a naval blockade.}}</ref>

==Types of blockade==

===Close, distant, and loose blockades===
A ''close'' blockade entails placing warships within sight of the blockaded coast or port, to ensure the immediate interception of any ship entering or leaving. It is both the most effective and the most difficult form of blockade to implement. Difficulties arise because the blockading ships must remain continuously at sea, exposed to storms and hardship, usually far from any support, and vulnerable to sudden attack from the blockaded side, whose ships may stay safe in harbor until they choose to come out.
[[File:Captured German U-boats outside their pen at Trondheim in Norway, 19 May 1945. BU6382.jpg|thumb|upright|In World War II, [[Nazi Germany|German]] [[U-boat]]s attempted to stop ships carrying food, supplies and [[materiel|''matériel'']] from reaching the United Kingdom, an example of a ''distant blockade''.]]

In a ''distant'' blockade, the blockaders stay well away from the blockaded coast and try to intercept any ships going in or out. This may require more ships on station, but they can usually operate closer to their bases, and are at much less risk from enemy raids. This was almost impossible prior to the 16th century due to the nature of the ships used.<ref>Palmer, Michael A., ''Command at Sea: Naval Command and Control since the Sixteenth Century'', Harvard University Press, Cambridge, 2005, p.22</ref>

A ''loose'' blockade is a close blockade where the blockading ships are withdrawn out of sight from the coast (behind the horizon) but no farther. The object of loose blockade is to lure the enemy into venturing out but to stay close enough to strike.

British [[admiral]] [[Horatio Nelson]] applied a loose blockade at [[Cádiz]] in 1805. The Franco-Spanish fleet under [[Pierre-Charles Villeneuve]] then came out, resulting in the [[Battle of Trafalgar]].<ref>Reynolds, Clark G. 1998. "Navies in History", p. 98. {{ISBN|1-55750-715-5}}.</ref>

===Pacific blockade===
Until 1827, blockades, as part of [[economic warfare]], were always a part of a war. This changed when France, [[Russian Empire|Russia]] and Britain came to the aid of the [[First Hellenic Republic|Greek rebels against Turkey]]. They blockaded the Turkish-occupied coast, which led to the [[battle of Navarino]]. War was never declared, however, so it is considered the first ''pacific'' — i.e. peaceful — blockade.<ref>Oppenheim, L. & Roxburgh, Ronald. 2005. "International Law: A Treatise", p. 53. {{ISBN|1-58477-609-9}}.</ref> The first truly [[pacific blockade]], involving no shooting at all, was the British blockade of the [[Republic of New Granada]] in 1837, established to compel New Granada to release an imprisoned British consul.<ref>''[[Encyclopædia Britannica]]'', 11th edition. 1911. "Pacific Blockade", vol. 20, p. 433-434.</ref>

==Legal status==
[[File:President Kennedy with advisors after EXCOMM meeting, 29 October 1962 crop.jpg|thumb|right|[[John F. Kennedy|President Kennedy]] and his advisors discuss the [[Cuban Missile Crisis]]. Part of the US response to [[Soviet Union|Soviet]] missiles being placed in [[Cuba]] was a naval blockade of the island.]]

Since 1945, the [[United Nations Security Council]] determines the legal status of blockades and by [[Chapter VII of the United Nations Charter|article 42]] of the [[United Nations Charter|UN Charter]], the council can also apply blockades.<ref>D'Amato, Anthony A. 1995. "International Law and Political Reality: Collected Papers", p. 138. {{ISBN|90-411-0036-9}}.</ref> The UN Charter allows for the right of self-defense but requires that this must be immediately reported to the Security Council to ensure the maintenance of international peace.

[[File:A 4-year-old Palestinian girl, lost her life due to malnutrition and lack of treatment due to the war on Gaza.jpg|thumb|left|Four year old Palestinian girl starved to death, during [[Gaza Famine]]]]
According to the not ratified document [[San Remo Manual]] on International Law Applicable to Armed Conflicts at Sea, 12 June 1994,<ref>{{cite web |url=http://www.icrc.org/ihl.nsf/FULL/560?OpenDocument |archive-url=https://web.archive.org/web/20060719010150/https://www.icrc.org/ihl.nsf/FULL/560?OpenDocument |url-status=dead |title=San Remo Manual on International Law Applicable to Armed Conflicts at Sea, 12 June 1994 |archive-date=19 July 2006 |website=ICRC.org}}</ref> a blockade is a legal method of warfare at sea but is governed by rules. The manual describes what can never be contraband. The blockading nation is free to select anything else as contraband in a list, which it must publish.

The blockading nation typically establishes a blockaded area of water, but any ship can be inspected as soon as it is established that it is attempting to break the blockade. This inspection can occur inside the blockaded area or in international waters, but never inside the territorial waters of a [[Neutrality (international relations)|neutral nation]].

A neutral ship must obey a request to stop for inspection from the blockading nation. If the situation so demands, the blockading nation can request that the ship divert to a known place or harbour for inspection. If the ship does not stop, then the ship is subject to capture. If people aboard the ship resist capture, they can be lawfully attacked.

===Act of war===
{{Main|Casus belli}}

According to modern international law, blockades are an act of war.<ref name=":0" /> In that sense, a blockade can be legal only if applied in the context [[self-defense]] – but never as part of a [[war of aggression]]. 

Blockades are illegal when used as to starve or to collectively punish a civilian population.<ref name=":1" /><ref name=":2" /><ref name=":3" /><ref name=":4" /><ref name=":5" /> In such cases, they are a [[war crime]] and potentially a [[crime against humanity]].<ref>{{cite journal |last1=Dannenbaum |first1=Tom |date=2021–2022 |title=Siege Starvation: A War Crime of Societal Torture |url=https://heinonline.org/HOL/LandingPage?handle=hein.journals/cjil22&div=25&id=&page= |journal=Chicago Journal of International Law |volume=22 |pages=368}}</ref><ref>{{cite web |title=Unlawful Blockades as Crimes Against Humanity {{!}} ASIL |url=https://www.asil.org/insights/volume/22/issue/5/unlawful-blockades-crimes-against-humanity |website=www.asil.org |language=en}}</ref>

== Blockade planning ==

Blockades depend on four general factors
[[File:Blockade connecticut plan civil war cartoon.jpg|thumb|A Northern cartoonist ridicules the [[Union (American Civil War)|Union]]'s initial attempts to blockade ports of the [[Confederate States of America|Confederacy]] in the [[American Civil War]]]]
* The '''value''' of the item being blockaded must warrant the need to blockade. For example, during the 1962 [[Cuban Missile Crisis]], the items to be blockaded (or "[[quarantine]]d" to use the more neutral term selected by President [[John F. Kennedy]]) were [[Medium-range ballistic missile]]s, capable of delivering [[nuclear weapon]]ry, bound for Cuba. Their value was high, as a military threat against the United States.
* The '''strength''' of the blockading force must be equal to or greater in strength than the opposition. The blockade is only successful if the 'thing' in question is prevented from reaching its receiver. For example, the overwhelming power of the [[Royal Navy]] allowed a successful [[Blockade of Germany (1914–1919)|blockade of Germany]] during and after World War I.
* '''Geography'''.  Knowing the routes of the enemy will help the blockader choose where to blockade: for example, a high [[mountain pass]] or a [[strait]] is a natural [[choke point]] and a candidate for [[fortification]].
* A blockade tends to be a long [[Military campaign|campaign]] requiring a '''long-term commitment''' by the blockading power. The [[Atlantic U-boat campaign of World War I]] and [[Battle of the Atlantic]] were essentially about German blockades, and lasted nearly as long as their respective wars.  The [[Imperial Japanese Navy]], however, made only sporadic efforts at blockade during the [[Pacific War]], preferring to seek victory by [[fleet action]].

==Blockade running==
{{main|Blockade runner}}
{{History of war}}
Blockade running is the practice of delivering cargo (food, for example) to a blockaded area. It has mainly been done by ships (called [[blockade runner]]s) across ports under naval blockade. Blockade runners were typically the fastest ships available and often lightly armed and armored. It is now also been done by aircraft, forming [[airbridge (logistics)|airbridges]], such as over the [[Berlin Blockade]] after [[World War II]].

==See also==
* [[Blockade of the Gaza Strip]]
* [[Blockade of Nagorno-Karabakh]]
* [[Command of the sea]]
* [[List of blockades]]
* [[Maritime Exclusion Zone]]
* [[No-fly zone]]
* [[Sea lines of communication]]
* [[Navicert]]

==References==
{{reflist}}
* {{cite EB1911|wstitle=Blockade}}

[[Category:Blockades| ]]
[[Category:Law of the sea]]
[[Category:Military strategy]]
[[Category:Military operations by type]]
[[Category:Economic warfare tactics]]