Missouri Compromise

Missouri Compromise, legislative measures enacted by the United States Congress in 1820 that regulated the extension of slavery in the United States for three decades. When slaveholding Missourians applied for statehood in 1818, the long-standing balance of free and slave states (11 each) was jeopardized. A northern-sponsored amendment was then attached to the bill (1819) authorizing statehood; it prohibited the entry of slaves into Missouri and provided for the gradual emancipation of those already there. The proslavery faction was unable to prevent the bill's passage by the House of Representatives, where free states held a majority, but southern strength in the Senate defeated the bill.

Maine, then a part of Massachusetts, also applied for statehood in 1819. Speaker of the House Henry Clay of Kentucky warned northern congressmen that unless they changed their position on Missouri the southerners would reject Maine's petition. To please the South the slavery restrictions for Missouri were then removed, and to satisfy the North, Senator Jesse B. Thomas (1777-1853) of Illinois introduced (February 1820) a proviso by which slavery would be prohibited forever from Louisiana Purchase territories north of 36° 30'. Southern extremists opposed any limit on the extension of slavery, but Clay maneuvered the measure through the House by a three-vote majority. Missouri and Maine were to enter statehood simultaneously to preserve sectional equality in the Senate. In 1821, when northern congressmen balked over antiblack clauses in Missouri's constitution, Clay again adjusted differences, and Missouri's admission was ensured.

The compromise became precedent for settling subsequent North-South disagreements over slavery and tariff issues, and it remained in effect until repealed by the Kansas-Nebraska Act of 1854.