Missouri Compromise — legislative compromise between pro- and anti-slavery parties in the run-up to the American Civil War

In February 1819, Representative James Tallmadge Jr. proposed amendments restricting slavery in Missouri's statehood bid, inflaming sectional tensions. The Senate was evenly split between eleven slave and eleven free states, meaning Missouri's admission as a slave state would tip the balance southward. Northern legislators cited the three-fifths clause as an existing constitutional inequality and argued Congress had an obligation to limit slavery's geographic spread.

The compromise deferred direct conflict over slavery for more than twenty years, though it entrenched a formal geographic division between free and slave territory. The Compromise of 1850 only briefly eased renewed tensions. The Kansas–Nebraska Act of 1854 effectively nullified the Missouri Compromise, and the Supreme Court struck it down in Dred Scott v. Sandford in 1857, accelerating the sectional crisis that culminated in the American Civil War.