The Missouri Compromise was a law designed to resolve whether the new state of Missouri would enter the United States as a free state or a slave state. A free state is one in which slavery is prohibited, and a slave state is one in which slavery is legal. At the time Missouri was going to enter the Union, the nation had an equal number of free and slave states. Northern states wanted Missouri to be a free state so they would have a majority in Congress. Southern states, for the same reason, wanted Missouri to be a slave state.
Senator Henry Clay promoted the Missouri Compromise, which Congress passed in 1820. The compromise was that Missouri entered the union as a slave state, and at the same time, Maine entered the union as a free state. As part of the compromise, Congress created an imaginary line at Missouri’s southern border. Congress said that any future new states north of that line would be free states. The conflict between allowing or prohibiting slavery in new states grew stronger in the following years. It became a big part of the sectionalism that caused the Civil War.
