On August 10, 1821, Missouri was formally admitted as the 24th state, completing the fraught political bargain known as the Missouri Compromise. The deal, engineered by Henry Clay, admitted Missouri as a slave state and Maine as a free state while banning slavery in the remaining Louisiana Territory north of the 36°30' parallel, a fragile balance that held for over three decades.
Missouri's application for statehood in 1819 ignited the first great sectional crisis over slavery's expansion, one that Thomas Jefferson, watching from retirement, called 'a fire bell in the night.' If admitted as a slave state, Missouri would tip the Senate's balance in favor of slaveholding interests; if free, it would anger the South. The debate raged for over a year, exposing fault lines that would eventually tear the country apart in 1861.
Henry Clay brokered the compromise: Missouri would enter as a slave state, Maine would be carved off from Massachusetts and admitted as a free state to preserve Senate parity, and a line would be drawn at 36°30' north latitude across the remaining Louisiana Purchase territory—slavery permitted south of it, prohibited north of it (except within Missouri itself, which lay mostly above the line).
Missouri's actual admission was delayed further when its proposed state constitution barred free Black people from entering the state, provoking another round of congressional fighting before a face-saving 'Second Missouri Compromise' allowed the state's admission. Missouri finally entered the Union on August 10, 1821. The compromise held until 1854, when the Kansas-Nebraska Act effectively repealed it, reigniting the sectional crisis that led directly to the Civil War.
Key people: Henry Clay, Thomas Jefferson