http://www.usmm.org/civilwar.html One of the first steps taken by the North against the Confederacy was establishment of a blockade of all southern seaports, thus cutting off imports of war materiel, medical supplies, and household goods. By preventing the sale of cotton abroad in exchange for war materiel, the Union blockade changed the balance of power in the war. The North conveniently forgot the War of 1812 was fought to defend the principle of freedom of the seas, and seized neutral ships trading with the South.