Missouri Compromise, 1820: The Missouri Compromise, adopted in 1820, kept the slave-state controversy under wraps for 34 years, until it was replaced by the Kansas-Nebraska Act of 1854. The Missouri Compromise kept the number of free and slave states balanced by admitting Maine as a free state, and Missouri as a slave state. The Missouri Compromise also banned slavery in the remainder of the Louisiana Territory located above the 36° 30' line of latitude. This is the report on the Missouri Compromise written by the conference committee.