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.