Answer:
The Missouri Compromise was passed in 1820 between the northern and southern states. It consisted of granting the state of Missouri slave status in exchange for the consent of the southern states that the western border of slavery would run along the parallel of 36° 30''. Whereas the border between free and slave states in the East of the continent was drawn along the Mason-Dixon Line and the Ohio River. In addition, a new state - Maine - was separated from Massachusetts to maintain a balance of power in the Senate between slave states and non-slavery states.
The Compromise arose from the need to maintain the balance that then existed between the 11 non-slave states (New Hampshire, Massachusetts, Connecticut, Rhode Island, New York, New Jersey, Pennsylvania, founders; and Vermont, Ohio, Indiana and Illinois, incorporated), and the other 11 slave states (Maryland, Delaware, Virginia, North Carolina, South Carolina, Georgia, founders; and Kentucky, Tennessee, Mississippi, Louisiana and Alabama, incorporated), discussing in 1819 the new admission law of the state of Missouri, a slave-territory, that would unbalance the composition of the Senate (each state had and has two representatives, regardless of its population), in favor of the slave states. In the House of Representatives there was no such balance because they were elected proportionally to the population, more numerous in the northern states.
