From Ohio History Central
The Missouri Compromise of 1820 maintained the balance among states favoring and opposed to slavery in the Congress of the United States.
In 1818, the Missouri Territory applied for statehood. Many Missourians wanted to allow slavery in their state. A number of Northerners opposed this idea for two reasons. First, abolitionist sentiment was growing in the North. Secondly, there were eleven free states and eleven slave states. For a bill to become a law, both houses of the United States Congress had to agree to it. With eleven slave and eleven free states, each side had the same number of senators. If Missouri became a slave state, the tie would be broken. The South would control the Senate and would be one step closer to legalizing slavery in states newly admitted to the Union. Because of their fears, Northern members of the United States Congress refused Missouri admittance to the United States as a slave state. When Maine applied for statehood in 1819 as a free state, Southern members of Congress threatened to prevent Maine's admittance.
Faced with deadlock, the Congress agreed to the Missouri Compromise in 1820. This agreement allowed Missouri to enter the United States as a slave state and Maine to enter as a free state. The Congress thus maintained the balance between slave and free states. To avoid additional conflicts in the future, the Congress also created the Missouri Compromise line. All future states north of Missouri's southern border would be free states. Future states south of Missouri's southern border would be slave states.
In Ohio, the Missouri Compromise was controversial. While, the Ohio legislature asked its national representatives to vote against slavery's expansion, some Ohioans came from the South and favored the growth of slaveholding states. Other people moved to the area from New England and tended to oppose slavery for both moral and economic reasons. There also was a growing abolitionist movement in Ohio, led primarily by the Society of Friends. Just as the nation was divided over slavery's expansion, so too were Ohioans.
The Missouri Compromise did not prevent future arguments from arising over slavery. The Missouri Compromise remained in effect until 1854, when the United States Congress passed the Kansas-Nebraska Act.