A navy imposes a blockade in order to isolate the enemy, or some part of his territory, from the rest of the world. In most wars the side with the stronger fleet tries to blockade the other side. Thus, the British Navy has blockaded among others, France, the United Stares, Germany, and most recently the Argentine forces in the Falkland Islands. The United States Navy has blockaded Mexico, the Confederacy, the Spanish forces in Cuba, Japan, and briefly, North Vietnam.
Still, William N. Jr
"A Naval Sieve: The Union Blockade in the Civil War,"
Naval War College Review: Vol. 36
, Article 5.
Available at: http://digital-commons.usnwc.edu/nwc-review/vol36/iss3/5