The Missouri Compromise occurred in 1820. Brokered by Henry Clay, this agreement admitted Maine to the United States as a free state and allowed Missouri to enter as a slave state but banned slavery in all other parts of the Louisiana Territory north of the 36th parallel.
The Missouri Compromise allowed the union to maintain an equal number of free states and slave states. Sectional tensions between the North, which was generally opposed to the extension of slavery, and the South, which favored extension, had been rising since the United States started to expand after the Revolutionary War. The Missouri Compromise remained the law of the land until 1856, when the Kansas-Nebraska Act of 1854 permitted settlers in some areas north of the 36th parallel to vote on whether their lands could admit slaves.