The result of the Missouri Compromise of 1820 was that Missouri was admitted into the union as a slave state, and Maine was admitted as a free state. In addition, a border was created across the Louisiana Territory, and slavery was banned in the northern party of the territory. The law remained in place until 1854 when it was repealed by the Kansas-Nebraska Act.
The Missouri Compromise came about as a way to keep the balance of power between the slave states and free states. Missouri wanted to join the union as a slave state, but anti-slavery factions in Congress were against it. Since Maine was also seeking to join the union, they created the Missouri Compromise, adding one slave state and one free state. In addition, an amendment to the compromise divided the Louisiana territory into a free region and a slave region.
The act was repealed by the Kansas-Nebraska Act of 1849. Kansas-Nebraska Act allowed for the states of Kansas and Nebraska, both which were north of the compromise line, to choose for themselves if they wanted to become slave states. In 1857, the Missouri Compromise was ruled unconstitutional because it violated the Fifth Amendment, which states that Congress was not allowed to deprive individuals of private property without due process.