Missouri Compromise

The Missouri Compromise was an act of the United States Congress passed in 1820 to resolve a crisis over the admission of Missouri as a slave state, which threatened to upset the balance between free and slave states in the Senate. It admitted Missouri as a slave state and, simultaneously, Maine as a free state, preserving that balance, and it prohibited slavery in the remaining Louisiana Purchase territory north of the 36 degrees 30 minutes parallel, Missouri's own southern border excepted. The compromise was engineered chiefly by House Speaker Henry Clay and held for over three decades as an uneasy truce on the expansion of slavery into new territories. It was effectively repealed by the Kansas-Nebraska Act of 1854, which reopened the question of slavery in those territories to popular sovereignty, and the Supreme Court declared the Missouri Compromise's territorial restriction unconstitutional in its 1857 Dred Scott decision.