How did the Missouri Compromise try to preserve the balance between free and slave states?

The Missouri Compromise of 1820 sought to maintain a political equilibrium between the North and the South by ensuring an equal number of free and slave states in the U.S. Senate.12

At the time, the Union consisted of 22 states, evenly divided between free and slave. When Missouri applied for statehood, a deadlock emerged in Congress over the expansion of slavery. To resolve this, Henry Clay engineered a legislative package that admitted Maine as a free state and Missouri as a slave state, thereby preserving the balance at 12 states each.12

Additionally, the compromise established a geographic boundary for the future of slavery: it prohibited the practice in the remainder of the Louisiana Purchase territory north of latitude 36°30′. While this measure temporarily averted a crisis, it failed to resolve the underlying moral and political conflicts regarding slavery, ultimately serving as a precursor to the American Civil War.12