A blockade is the act of actively preventing a country or region from receiving or sending food, supplies, weapons, or communications, and sometimes people, by military force. A blockade differs from an embargo or sanctions, which are legal barriers to trade. 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.
While most blockades historically took place at sea, blockades are also used on land to prevent entrance of an area. For example, Armenia is a landlocked country that Turkey and Azerbaijan blockade. Accordingly, Armenia cannot use these countries' air or land space for international trade, and Armenia mainly uses its northern borders to trade. As a result, the country's economy cannot function on a full scale and distracts the country's economic development.
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 the blockade 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 jamming radio signals and severing undersea cables.