[382]
During his presidency, Jefferson allowed the diffusion of slavery into the Louisiana Territory hoping to prevent slave uprisings in Virginia and to prevent South Carolina secession.[383] In 1804, in a compromise on the slavery issue, Jefferson and Congress banned domestic slave trafficking for one year into the Louisiana Territory.[384] In 1806 he officially called for anti-slavery legislation terminating the import or export of slaves. Congress passed the law in 1807.[375][385][386]
In 1819, Jefferson strongly opposed a Missouri statehood application amendment that banned domestic slave importation and freed slaves at the age of 25 on grounds it would destroy the union.[387]  In Notes on the State of Virginia, he created controversy by calling slavery a moral evil for which the nation would ultimately have to account to God.[388] Jefferson wrote of his "suspicion" that Black people were mentally and physically inferior to Whites, but argued that they nonetheless had innate human rights.[375][389][390] He therefore supported colonization plans that would transport freed slaves to another country, such as Liberia or Sierra Leone, though he recognized the impracticability of such proposals.