The Missouri Compromise, also known as the Compromise of 1820, was a federal legislation of the United States that balanced desires of northern states to prevent the expansion of slavery in the country with those of southern states to expand it. It admitted Missouri as a slave state and Maine as a free state and declared a policy of prohibiting slavery in the remaining Louisiana Purchase lands north of the 36°30′ parallel. The 16th United States Congress passed the legislation on March 3, 1820, and President James Monroe signed it on March 6, 1820.
The Missouri Compromise was very controversial, and many worried that the country had become lawfully divided along sectarian lines. The Kansas–Nebraska Act effectively repealed the bill in 1854, and the Supreme Court declared it unconstitutional in Dred Scott v. Sandford (1857), both of which increased tensions over slavery and contributed to the American Civil War.