Missouri Compromise (1820): Slavery and the Balance of States

The Missouri Compromise was a series of measures passed by the United States Congress in March 1820 to settle a bitter national dispute over whether Missouri should join the Union as a slave state. It admitted Maine as a free state and Missouri as a slave state, and banned slavery in the rest of the Louisiana Purchase north of latitude 36°30’. The deal kept the peace for over three decades but exposed how deeply slavery divided the country.

Background

By 1819 the United States had 22 states, evenly split between 11 free states in the North and 11 slave states in the South. In the House of Representatives the faster-growing North already had a majority, so the equal balance in the Senate gave the slave states a crucial veto over national policy.

Missouri, part of the vast territory bought from France in 1803, had been settled largely by migrants from the upper South, many of whom brought enslaved people with them. By 1819 around 10,000 enslaved people lived there, and Missouri applied for statehood with slavery legally in place.

Missouri would also be the first state lying entirely west of the Mississippi, in Louisiana Purchase lands. Its admission would set a precedent for the enormous lands still to be organised in the West.

The Tallmadge Amendment

In February 1819 Representative James Tallmadge Jr. of New York proposed an amendment to the Missouri statehood bill. It would have banned bringing more enslaved people into Missouri and freed the children born to enslaved parents after admission when they reached the age of 25.

The House, with its Northern majority, passed the amendment in votes that split almost exactly along sectional lines. The Senate rejected it, and Congress adjourned without a decision. When it met again in December 1819 the debate was even more intense. Senator Rufus King of New York argued that Congress had the power to bar slavery from new states, while Southern members insisted that the Constitution gave Congress no right to impose such conditions.

The compromise

A solution emerged by linking Missouri to Maine, then part of Massachusetts, which had also applied for statehood. Admitting both would keep the Senate balance at 12 free and 12 slave states.

Senator Jesse B. Thomas of Illinois proposed adding a ban on slavery in all the remaining Louisiana Purchase territory north of 36°30’, the line of Missouri’s southern border, except within Missouri. The Senate combined the measures. In the House, the key vote to remove the restriction on slavery from the Missouri bill passed narrowly, 90 to 87, while the 36°30’ line passed easily. Speaker Henry Clay managed the votes skilfully, earning him the nickname the Great Pacificator.

President James Monroe, after consulting his cabinet on whether the line was constitutional, signed the Missouri bill on 6 March 1820. Maine became the 23rd state on 15 March 1820.

The second crisis

The dispute flared again when Missouri’s new constitution, drafted in 1820, required the legislature to bar free Black people and people of mixed race from entering the state. Many Northerners argued this violated the Constitution’s guarantee that citizens of each state were entitled to the privileges of citizens in every state, since some Northern states recognised Black citizens.

Clay arranged a second compromise in early 1821. Missouri would be admitted on condition that its constitution would never be interpreted to deny any citizen’s constitutional rights. The Missouri legislature gave a vague pledge, and Missouri became the 24th state on 10 August 1821.

Many leaders saw the crisis as a warning. Thomas Jefferson, writing in April 1820, famously compared the dispute to “a fire bell in the night” that filled him with alarm for the Union. John Quincy Adams, then Secretary of State, privately described it as a preface to a much larger conflict.

The compromise did not settle the moral question of slavery. Instead it set a geographical rule and confirmed the idea that the Senate balance between free and slave states must be maintained. That idea encouraged both sections to compete for new territory.

Unravelling

The arrangement held for about 30 years, but westward expansion revived the dispute. The annexation of Texas and the Mexican-American War added huge lands south and west of the old line, leading to the Compromise of 1850. In 1854 the Kansas-Nebraska Act repealed the 36°30’ restriction and let settlers decide on slavery, which led directly to the violence of Bleeding Kansas.

In 1857 the Supreme Court ruled in the Dred Scott case that Congress had no power to prohibit slavery in the territories, which meant the Missouri Compromise ban had been unconstitutional. Within four years the Union had split and the Civil War had begun.

Key people

Henry Clay of Kentucky, Speaker of the House, was the most important broker of both the 1820 and 1821 settlements, though he did not invent the 36°30’ line. James Tallmadge Jr., a New York congressman, triggered the crisis with his amendment and left Congress soon afterwards. Jesse B. Thomas, a senator from Illinois with ties to the South, proposed the geographical line that made a deal possible. Rufus King of New York, a signer of the Constitution, led the Northern case in the Senate. President James Monroe, a Virginian slaveholder, accepted the compromise as the price of national unity.

The debate and its arguments

The debates in Congress went far beyond Missouri. Northern speakers argued that the founders had hoped slavery would gradually disappear and pointed to the Northwest Ordinance of 1787, which had barred slavery north of the Ohio River. Some also complained about the three-fifths clause of the Constitution, which counted enslaved people toward Southern representation in Congress.

Southern speakers replied that new states must enter the Union on equal terms with the old ones and that Congress could not limit a state’s control over its own institutions. Some argued that spreading slavery westward would thin out the enslaved population and make eventual emancipation easier, a theory known as diffusion. For the first time, members openly warned that disunion and civil war could follow.

Myths and facts

The compromise is often described as a single law, but it consisted of separate acts passed in 1820 and a further resolution in 1821. It is also sometimes thought to have banned slavery everywhere north of 36°30’. In fact the line applied only to the unorganised Louisiana Purchase lands; it did not affect existing states, and Missouri itself lay almost entirely north of the line.

Timeline

• 1819, 13 February: James Tallmadge Jr. introduces his amendment to the Missouri bill.
• 1819, March: Congress adjourns deadlocked after the Senate rejects the amendment.
• 1819, 14 December: Alabama becomes a state, making 11 free and 11 slave states.
• 1820, February: Senate links Maine and Missouri and adds the 36°30’ line.
• 1820, 6 March: President James Monroe signs the Missouri bill.
• 1820, 15 March: Maine becomes the 23rd state.
• 1821, late February–March: Congress approves the second Missouri compromise.
• 1821, 10 August: Missouri becomes the 24th state.

Why it matters

The Missouri Compromise was the first great national crisis over slavery after independence. It showed that slavery could split the political system along sectional lines, and its solution, dividing the West by a line, only postponed the struggle that ended in the Civil War.