A blockade is an act in which a state or an international actor prevents goods, communications, and people from accessing or exiting an enemy’s territory, whether by land, sea, or air. Blockades are usually enforced to restrict the actions of a state, rather than just the city or port that the blockade might take place in. The history of blockades can be traced back to the Peloponnesian Wars, with the Spartans blockading the city of Athens. Modern examples of blockades are more sophisticated and include the Berlin Blockade in the late 1940s and the Blockade of the Gaza Strip, which is still being enforced. A traditional blockade, with regard to legality, has to be formally declared and effective. Effective in this sense means that the blockade must be properly imposed by a sufficient force to prevent the enemy from replenishing itself through outside resources. In Article 42 of the Charter of the United Nations, which was ratified in 1945, the United Nations Security Council declared blockades a legal action that may be necessary to maintain or restore international peace and security. Security refers to being free from risk or danger and taking the appropriate measures to provide for a secure or safe environment, and blockades serve as a mechanism for ensuring national or global security against a threatening enemy.


Historically, blockades have been used as a strategic tool during war, consisting mainly of naval ships blocking and obstructing entrance to or exit from a state. Most historians have come to a consensus that the first significant blockade occurred in the second Peloponnesian War from 431 to 404 BCE, fought between Athens and Sparta, with Sparta ultimately emerging as the victor. An important aspect of the war that helped Sparta to victory was the blockade of the Athenian port of Piraeus. The Athenians built vast walls from the city of Athens to the port so that cargo and resources could be safely brought to the city. The Spartans put a blockade on the port, which cut off supplies to Athens, resulting in starvation in the city. Athens surrendered a year later to save its people from further suffering.

Blockades were conducted in this manner throughout history to force an enemy to surrender, and another prominent example of this occurred during the Revolutionary War between the American colonies and England. The Battle of Yorktown was won by the colonies, with a large amount of help from the French, which led to the British surrendering in the war. Lord Cornwallis arrived in Yorktown to await fresh supplies from Britain. Meanwhile, George Washington led his troops south from New York to Yorktown, and the French fought the British in the Chesapeake Bay. The French took control of the bay, which led to a French blockade that did not allow Lord Cornwallis to receive any supplies or any route of escape. Cornwallis had no choice but to surrender, leading to the end of the war.

Legal Status

Blockades, for the most part, have changed due to the dynamic climate in which actors now engage with one another. The Security Council defines blockades in a traditional sense; in recent years, blockades have become harder to apply, and there are questions regarding the legality of modern blockades. As noted earlier, a blockade must be declared and effective to be legal and binding. This aspect still applies through the San Remo Manual on International Law Applicable to Armed Conflicts at Sea, adopted in 1994 as part of round table discussions by legal and naval experts. Article 42 of the Charter of the United Nations gives the Security Council the power to use blockades as necessary to provide adequate peace and security for members of the United Nations. The emergence of humanitarian law has strained the use of blockades because starving civilians of another state would violate this kind of law. While the military advantage that blockades can offer is substantial, the backlash in abusing humanitarian law can negate this advantage. Blockades have shifted from being enforced strictly by sea to also include land and air blockades and blocking or jamming electronic communications. This is part of the dynamic climate that now exists in the world, consistent with recent examples of blockades.

The significance of legal definitions of blockade can be made apparent by noting that the John F. Kennedy administration announced that its efforts to isolate Cuba during the Cuban Missile Crisis in 1962 should be officially referred to as a “quarantine” rather than a “blockade.” President Kennedy noted that a blockade indicated a state of war and thus utilized the term quarantine in an attempt to de-escalate the tensions and to reach out to Cuba diplomatically.

Recent Examples

The Berlin Blockade is a good example of a blockade that was ineffective due to a constantly changing security environment in which technological improvements are always being made. The blockade was started in the summer of 1948 by Soviet forces in fear of Berlin falling into the hands of the Allies of World War II. The Soviet Union blockaded rail, road, and water access to the western portion of Berlin. In response to this blockade and the crisis in Berlin, the United States and the United Kingdom airlifted food, fuel, and other supplies to Berlin from West Germany. The crisis ended the next year due to the efficiency of the airlift in aiding Berlin. The lesson learned from this blockade is that states now have the resources and technology to bypass land and sea blockades; blockades must also be enforced through the air.

The blockade of the Gaza Strip is in reaction to Hamas taking over political control of the strip in 2007. Israel, with the support of Egypt, has enforced this blockade by sea, land, and air since 2007. The blockade has prevented the movement of goods and people between the Gaza Strip and the West Bank. Israel has strategically placed this blockade to ensure that the people of Gaza do not starve, in order to prevent action from the international community on behalf of humanitarian law. Balancing the effectiveness of the blockade and the security of Israel has been vital to the blockade maintaining its legitimacy, as Israel regularly makes claims of the need for border protection from Hamas. As blockades continually evolve from being coordinated naval efforts into complex land, sea, and air endeavors, it is up to states and the international community to oversee blockades in accordance with conflict and humanitarian law, while also gaining the strategic advantages that blockades have to offer.


Blockades have a long, rich history in the quest for national security. Modern international law has had an impact on the method and limits of a blockade, but the continued use of blockades indicates that they remain as policy choices for governments seeking security options.

Tobias T. Gibson and Caleb Marquis

See also Port Security

Further Readings

Spelman, Elizabeth. “The Legality of the Israeli Naval Blockade of the Gaza Strip.” Web Journal of Current Legal Issues, v.19/1 (2013). (Accessed December 2014).

United Nations. “Charter of the United Nations.” (Accessed December 2014).

U.S. Department of State, Office of the Historian. “The Berlin Airlift, 1948–1949” (October 31, 2013). (Accessed December 2014).

U.S. Department of State, Office of the Historian. “The Cuban Missile Crisis, October 1962” (October 31, 2013). (Accessed January 5, 2015).