Slavery was confirmed by statute or royal decree in all the English, Spanish, and French colonies of North America. After American Independence, slavery therefore enjoyed a legal existence in all the states. In the NORTHWEST ORDINANCE of 1787, the Confederation Congress prohibited slavery in the Northwest Territory, although it also provided for the recapture of slaves escaping there. The First Congress reenacted this ban, but in legislation for the area southwest of the Ohio River it omitted the exclusion of slavery, so that slavery was free to penetrate into the TERRITORIES ceded by Virginia, New York, North Carolina, South Carolina, and Georgia. Slavery also existed in the French settlements that were to become Louisiana, Missouri, Illinois, and Indiana. The treaty of cession with France (1803), by which the United States acquired the LOUISIANA PURCHASE, guaranteed extant property rights, thus assuring slavery's perpetuation in those territories.
Despite the ban of the Northwest Ordinance, settlers in Ohio (particularly in the Virginia Military Reserve in the southwest quadrant of the territory), Indiana, and Illinois tried to introduce slavery, with the connivance of Indiana territorial governor William Henry Harrison in the case of Ohio, and at least the tacit consent of President THOMAS JEFFERSON. They failed in Ohio and Indiana, but in Illinois slavery continued in subterfuge forms in the lead mines of Galena and the salt mines of Shawneetown, and only a vigorous abolitionist effort prevented its legalization throughout the state in 1822.
The Constitution contained no direct allusion to slavery in the territories; the new states and territories clauses did not refer to it, although the fugitive slave clause permitted recapture of fugitives only from the states, not the territories. Consequently, when Missouri sought admission as a slave state in 1819, Congress had no textual guidance, and for the first time it had to extrapolate from what it could determine of the Framers' intent concerning the territories. The result was a long and bitter debate in which restrictionists argued that slavery was hostile to the spirit of republican government and should not be extended to the new lands, while slavery's supporters insisted that Congress lacked power to exclude slavery from any territory. Jefferson at the time joined the antirestrictionists, arguing that as slavery spread it would diffuse to the point where the black population, relative to the white, would dwindle in both the old states and the new territories. The Missouri controversy was settled by admitting Missouri as a slave state and Maine as a free state, while prohibiting slavery in all the Louisiana Purchase territory north of Missouri's southern boundary (3630). (See MISSOURI COMPROMISE.) Jefferson likened the Missouri debates to a "firebell in the night," the "knell of the union."
As the confrontation over slavery intensified in the 1830s, abolitionists and defenders of slavery amplified their constitutional and policy arguments about slavery's future in the territories. Abolitionists found two sources of congressional power to exclude slavery. They saw the territories clause (Article IV, section 3) as a plenary grant of...