In the years leading up to the Missouri Compromise of 1820, tensions began to rise between pro-slavery and anti-slavery factions within the U.S. Congress and across the country. They reached a boiling point after Missouri’s 1819 request for admission to the Union as a slave state, which threatened to upset the delicate balance between slave states and free states. To keep the peace, Congress orchestrated a two-part compromise, granting Missouri’s request but also admitting Maine as a free state. It also passed an amendment that drew an imaginary line across the former Louisiana Territory, establishing a boundary between free and slave regions that remained the law of the land until it was negated by the Kansas-Nebraska Act of 1854.