Lincoln did not "blockade" any foreign ports, as recognized under international law. The confederates like to put the cart before the horse, and claim
because Lincoln used the term "blockade" in his April 1861 Proclamation, he therefore "recognized" the CSA as a legitimate entity. Lincoln simply closed the insurrectionist-controlled ports to traffic and notified the rest of the world that their shipping entered them at their own risk.
The Supreme Court supported Lincoln and his interpretation of the "blockade" in the Prize Cases. Even the Taney minority did not put up much of a fuss on that point.
Thanks.
Paludan in his work (The Presidency of Abraham Lincoln) stated that the problem was the word used, blockade.
Nations do have a right to close their ports.
Jefferson did so when he tried to keep us neutral during the war between France and England.