while jefferson was president, congress prohibited the importation of slaves, effective 1808. although smuggling (illegal importing) through spanish florida was common. slave trading within the united states, however, continued at a fast pace. this was because there was a need for labor due to the creation of cotton plantations in the deep south. new communities of african-american culture were created in the deep south. there were 4 million slaves in the deep south before they were set free.