Answer:
In 1820, the United States Congress passed the Missouri Compromise, which was a set of laws. Under the terms of the Missouri Compromise, Missouri was admitted as a slave state, but slavery was not allowed in the rest of the Louisiana Territory north of the 36°30' parallel. This area became known as the "free territory."
The compromise was made because of the growing tension between people in the United States who were for and against slavery. The balance of power between free and slave states in Congress could have been upset if Missouri became a slave state. The compromise was made to keep that balance.
At the time, the compromise was controversial because it effectively divided the free states from the slave states and didn't do much to solve the problem of slavery in the United States. Still, it kept the United States together for a few more decades, until the issue of slavery came up again in the years before the American Civil War.
Under the terms of the Missouri Compromise, the state of Missouri was allowed to have slavery, as it was admitted as a slave state. In addition to Missouri, slavery would have been allowed in any state south of the 36°30' parallel, which included Arkansas, Florida, Georgia, Alabama, Louisiana, Mississippi, and South Carolina. However, slavery was prohibited in the remaining portion of the Louisiana Territory north of the 36°30' parallel, which included the present-day states of Iowa, Illinois, Indiana, Michigan, Ohio, Wisconsin, and parts of Minnesota.