The argument over whether slavery should be legal in the united states became heated when, in 1817, missouri applied to become a state. at the time, there were an equal number of states that did not support slavery as there were states that did. slavery was legal in missouri, so if it joined the union, there would no longer be a balance. the missouri compromise was reached, which stated that maine would be accepted as a free state, and missouri would be a slave state. from then on, slavery was banned from the territories north of missouri’s border. this compromise seemed to settle the issue. however, the conflict between the north and south over slavery continued to worsen. which sentence best states the main idea of the passage? the missouri compromise settled the argument between free states and slave states. the missouri compromise kept the balance between free and slave states, but the argument over slavery continued. the missouri compromise settled the issue of slavery by banning slavery in territory north of the missouri border. the missouri compromise allowed missouri and maine to become states in the union.