Blockade

A blockade is a belligerent operation that bars ingress and egress to an enemy coast or port, lawful under the law of naval warfare only if it is declared, notified, effective, and impartially applied to all flags. The effectiveness requirement, codified from the 1856 Paris Declaration and restated in the San Remo Manual, distinguishes a true blockade from a mere paper declaration. A blockade is an act of war; it differs from peacetime interdiction or quarantine, which rest on different legal authorities.