Congress passed and Jefferson signed legislation ending the legal importation of enslaved Africans into the United States, taking effect January 1, 1808 — the earliest date permitted under the Constitution's twenty-year moratorium on such a ban. The law did nothing to end slavery itself, and a thriving domestic slave trade continued to grow for decades afterward.
The Constitution's framers had struck a grim bargain in 1787: Congress could not prohibit the importation of slaves before 1808, a concession to South Carolina and Georgia delegates who insisted on continued access to the trade. Jefferson, despite owning hundreds of enslaved people himself, called for the ban in his 1806 annual message to Congress, and lawmakers moved to pass it as soon as constitutionally possible.
The law imposed fines and forfeiture on ships caught importing captives, though enforcement was patchy and smuggling persisted, particularly into Louisiana and the Gulf Coast. Britain would abolish its own slave trade that same year, and the two nations later cooperated, however imperfectly, in suppressing the international trade.
Crucially, the act did not free a single enslaved person already in America, nor did it stop the trade in human beings within the country's borders. Instead, the domestic slave trade — driven by the cotton boom and westward expansion — exploded in the decades that followed, with hundreds of thousands of enslaved people forcibly marched or shipped from the Upper South to Deep South plantations.