A military tactic through which ports are shut off to keep people or supplies from moving in or out

A military tactic through which ports are shut off to keep people and or supplies from moving in or out is called a blockade. A blockade is usually directed at an entire country or region and is different from a siege which targets a fortress or a city. It is also distinct from an embargo or sanctions, which are actually legal barriers to trade.

While most blockades in history took place at sea, blockades were also used on land to prevent someone from coming into a certain area. 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.