The U.S. Congress prohibited the importation of slaves into any port or place within the jurisdiction of the United States from any foreign kingdom, place or country.
This is something that I bring up when I portray a federal sailor. Many people don't know that there were MAJOR efforts to end slavery as well as the slave trade YEARS before the Civil War.
As a older fellow, who wears the blue portraying a union sailor it would have been very likely that I would have served in the African Squadron to suppress the slave trade if I have served in the Navy for a long period of time before the war.
Again, the study of history with it's many diverse paths is endlessly fascinating.