When the Missouri Territory applied for statehood in 1818, the United States had an equal number of free states and slave states. The territory's leaders wanted Missouri to be a slave state. But that would have destroyed the balance of representation in Congress. A heated debate broke out. The southern representatives and Missouri's leaders thought states should be able to decide the slavery question for themselves. Northern members of Congress thought otherwise. Would the Union split apart over the question of slavery? The Missouri Compromise settled the argument and saved the Union—temporarily. So why was the Missouri Compromise of 1820 so controversial? Who was the great compromiser? What were the terms of the Missouri Compromise? Discover the facts about one of the most debated compromises in U.S. history.