In 1820, after angry debate in Congress, Missouri entered the Union as a slave state, and Maine was admitted as a free state to preserve the balance of slave and free states in the Union. Also, slavery was banned from that part of the Louisiana Territory north of 36° 30'.
The Missouri Compromise, also called the Compromise of 1820, was an agreement passed in 1820 between the pro-slavery and anti-slavery factions in the United States Congress, involving primarily the regulation of slavery in the western territories. It prohibited slavery in the former Louisiana Territory north of the parallel 36°30' north except within the boundaries of the proposed state of Missouri. Prior to the agreement, the House of Representatives had refused to accept this compromise and a conference committee was appointed.