In basic terms, the north states didn't want slaves and the south states did. The boundary line deciding if a state was north or south, was the Ohio river. Anything below that automatically became a south state. The problem was that the House of Representatives is based off of the population of a state, so if Missouri became a state, the balance between north and south representatives would be thrown off. The Missouri compromise cut the boundary line straight down the middle, so that the north side of Missouri would have north representatives and visa versa.
The issue of admitting Missouri to the union precipitated a major crisis due to the dispute over slavery. The Missouri Compromise was essentially a temporary fix aimed at preserving balance between North and South and preventing the escalation of sectional conflict. However, later territorial acquisitions and the concept of popular sovereignty reignited the sectional conflicts over slavery, showing that the Compromise was more of a truce than a resolution. ;
The admission of Missouri as a state precipitated a major crisis due to the conflict over slavery, as it threatened the balance of power between slave and free states in the Senate. The Missouri Compromise of 1820 allowed Missouri to enter as a slave state and Maine as a free state, maintaining this balance and setting a geographic boundary for slavery. Though a temporary solution, it highlighted the increasing division over slavery that would eventually lead to deeper conflicts in the U.S.
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