Missouri Compromise Summary

March 6, 1820

The Missouri Compromise comprised legislation passed by the U.S. Congress in 1820 that attempted to resolve sectional disputes over the extension of slavery in western territories of the United States.

Henry Clay, Portrait, Brady

Henry Clay is often given credit for the passage Missouri Compromise because he used his considerable influence as Speaker of the House of Representatives to forge a consensus in Congress. Image Source: Library of Congress.

Events Leading Up to the Missouri Compromise of 1820

When delegates to the Constitutional Convention assembled in Philadelphia in 1787, one of the more daunting tasks that they faced was resolving sectional differences between the North and South centered on the issue of slavery. After weeks of debate proved futile, the delegates negotiated a series of compromises that enabled them to proceed with their primary assignment of forming “a more perfect Union” between the separate states.

In the short term, the compromises regarding the status of slavery established in the Constitution facilitated the creation of the new republic (at the expense of blacks held in bondage), but they also sowed the seeds of turmoil that began coming to fruition as the nation expanded west in the coming decades.

The Northwest Ordinance

As the delegates to the Constitutional Convention set about creating a new government, representatives to the Congress of the existing government established under the Articles of Confederation, known as the Confederation Congress, were meeting in New York. On July 13, 1787, the Confederation Congress enacted the Northwest Ordinance, which stipulated “There shall be neither slavery nor involuntary servitude in the said territory,… ” The Northwest Ordinance established the Ohio River as the border separating free and slave states between the Appalachian Mountains and the Mississippi River. For the next three decades, that boundary forestalled major sectional disputes over slavery.

The Louisiana Purchase

Circumstances changed in 1803 when Napoleon Bonaparte sold President Thomas Jefferson 828,000 square miles of land west of the Mississippi River. The Louisiana Purchase created new challenges for the federal government. Besides land ownership issues regarding the native inhabitants, Congress eventually had to address the question of the expansion of slavery in the new territory.

Missouri Statehood

In 1812, Congress carved the Missouri Territory out of the Louisiana Purchase. Settlers began pouring into the new territory, many of them slaveholders from the South. In 1818, when the residents of Missouri petitioned Congress for statehood, roughly 8,000 to 10,000 slaves lived in the territory.  In January, residents of the territory petitioned the U.S. House of Representatives for statehood, but the House did not consider the measure during that session. In December 1818, Missouri residents petitioned Congress for statehood a second time.

The Tallmadge Amendment

The House took up the request during the next session. Southerners expected Congress to admit Missouri as a slave state, but on February 13, 1819, New York Congressman James Tallmadge introduced an amendment to the Missouri statehood measure that would gradually end slavery in the new state. The Tallmadge Amendment also mandated the emancipation of all children of slaves born in the State of Missouri upon reaching the age of twenty-five. The Tallmadge Amendment started a year of bitter debate in both houses of Congress. On February 17, 1819, the House passed a bill recommending Missouri statehood, including the Tallmadge Amendment, by a vote of 82 to 78, and forwarded it to the Senate. The upper chamber never voted on the proposed legislation.


During the following session of Congress, on January 3, 1820, the House passed legislation to admit Maine to the Union as a free state. Later that month, the lower chamber revisited the proposal for Missouri statehood. On January 26, 1820, John W. Taylor of New York introduced an amendment allowing Missouri to enter the union as a slave state, which the House adopted.

The Senate tied the two bills together, passing a single bill admitting Maine to the Union and an amendment enabling the people of Missouri to draft a state constitution. The proposed legislation hinged upon an important second amendment introduced by Senator Jesse B. Thomas of Illinois. The original bill provided for a trade-off: admitting Maine as a free state in return for admitting Missouri as a slave state, thus maintaining the balance of power in the Senate (twelve free states and twelve slave states). As amended by Thomas, however, the bill also prohibited slavery in the rest of the Louisiana Territory, north of the southern border of the new state (36°30′ north latitude). The Senate passed the amended legislation and returned it to the House.

The amended Senate bill evoked considerable sectional rancor in the lower chamber. House Speaker Henry Clay had to use his considerable skills to forge a consensus. Eventually, he got his colleagues to enact two bills—one admitting Maine to the Union and another, which included the Thomas Amendment, enabling the citizens of Missouri to draft a state constitution with no restrictions upon slavery. Together, the two pieces of legislation became known as the Missouri Compromise. Congress passed the compromise legislation on March 5, 1820, and President James Monroe signed it into law the next day.

A Second Compromise

Missouri’s statehood request required a second compromise after Missouri submitted its state constitution to Congress in 1821. The proposed constitution contained a provision that excluded “free negroes and mulattoes” from the state. Once again, Clay demonstrated his abilities as the “Great Compromiser” by getting the Congress to allow the admission of Missouri to the Union provided that the exclusionary clause in the proposed constitution “shall never be construed to authorize the passage of any law . . . by which any citizen of either of the States in this Union shall be excluded from the enjoyment of any of the privileges and immunities to which such citizen is entitled under the Constitution of the United States.” Thus, by agreeing to never deny citizens of other states coming into Missouri, the rights afforded them by the U.S. Constitution, Missouri became the 24th state on August 10, 1821.


Besides settling the issues at hand, namely the admission of the states of Missouri and Maine to the Union, the Missouri Compromise had other important consequences. It temporarily muffled the debate over slavery (or at least the extension of slavery) in the United States, although the abolitionist movement continued to grow in the North. Beyond that, it also established the precedent that Congress could regulate slavery in the territories even though the Constitution did not address the issue. Three decades later, that precedent became the focal point of constitutional and states’ rights arguments that contributed to the attempted dissolution of the Union in 1860.

The slavery issue reached crisis proportions once again in 1850 when Congress struggled over the disposition of new territories acquired during the Mexican-American War. The Compromise of 1850, authored by Clay and shepherded through Congress by Illinois Senator Stephen Douglas, formally codified the concept of popular sovereignty, which Douglas and Michigan Senator Lewis Cass championed.

In 1854, the Kansas-Nebraska Act — which also invoked popular sovereignty — gutted the key provision of the Missouri Compromise regarding slavery in the Missouri Territory.

Three years later, the U.S. Supreme Court’s decision in the case of Dred Scott v. Sandford, nurtured the growth of the Republican Party, alienating Southerners even more. The election of Abraham Lincoln to the presidency in 1860, proved to be the death knell of the spirit of compromise. Ultimately, only the tragedy of four years of civil war would determine the future of the Union, and slavery in the United States.

Citation Information

The following information is provided for citations.

  • Article Title Missouri Compromise Summary
  • Date March 6, 1820
  • Author
  • Keywords missouri compromise, jesse burgess Thomas, henry clay, james Tallmadge, john w. taylor
  • Website Name American History Central
  • Access Date September 26, 2023
  • Publisher R.Squared Communications, LLC
  • Original Published Date
  • Date of Last Update December 17, 2022

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