The internal slave trade in the United States, also known as the domestic slave trade, the Second Middle Passage and the interregional slave trade, was the mercantile trade of enslaved people within the United States. It was most significant after 1808, when the importation of slaves from Africa was prohibited by federal law. Historians estimate that upwards of one million slaves were forcibly relocated from the Upper South, places like Maryland, Virginia, Kentucky, North Carolina, Tennessee, and Missouri, to the territories and states of the Deep South, especially Georgia, Alabama, Louisiana, Mississippi, Arkansas, and Texas.
Economists say that transactions in the inter-regional slave market were driven primarily by differences in the marginal productivity of labor, which were based in the relative advantage between climates for the production of staple goods. The trade was strongly influenced by the invention of the cotton gin, which made short-staple cotton profitable for cultivation across large swathes of the upland Deep South (the Black Belt). Previously the commodity was based on long-staple cotton cultivated in coastal areas and the Sea Islands.