An Act Prohibiting Importation of Slaves became effective on January 1, 1808. It was passed in March 1807 and was the first law prohibiting the importation of slaves into the United States. First the Treasury Department, then the Secretary of the Navy, and at times the Secretary of State were responsible for enforcing the law. Although it was poorly enforced, the law helped to end slavery in the United States by prohibiting the transportation of slaves from Africa to the United States and its territories. It prompted some Southern states to pass similar laws, while other states refused to act.