The Missouri Compromise is signed into law by United States President James Monroe. The compromise allows Missouri to enter the Union as a slave state, brings Maine into the Union as a free state, and makes the rest of the northern part of the Louisiana Purchase territory slavery-free.

The Missouri Compromise was federal legislation of the United States that balanced the desires of northern states to prevent the expansion of slavery in the country with those of southern states to expand it. It admitted Missouri as a slave state and Maine as a free state and declared a policy of prohibiting slavery in the remaining Louisiana Purchase lands north of the 36°30′ parallel. The 16th United States Congress passed the legislation on March 3, 1820, and President James Monroe signed it on March 6, 1820.