A more troubling pattern was also emerging in national politics and culture. During the first decades of the nineteenth century, American politics was shifting toward “sectional” conflict among the states of the North, South, and West.

Since the ratification of the Constitution in 1789, the state of Virginia had wielded more influence on the federal government than any other state. Five of the first six presidents, for example, were from Virginia. Immigration caused by the market revolution, however, caused the country’s population to grow fastest in northern states like New York. Northern political leaders were becoming wary of what they perceived to be a disproportionate influence in federal politics by Virginia and other southern states.

Furthermore, many northerners feared that the southern states’ common interest in protecting slavery was creating a congressional voting bloc that would be difficult for “free states” to overcome. The North and South began to clash over federal policy as northern states gradually ended slavery but southern states came to depend even more on slave labor.

The most important instance of these rising tensions erupted in the Missouri Crisis. When white settlers in Missouri, a new territory carved out of the Louisiana Purchase, applied for statehood in 1819, the balance of political power between northern and southern states became the focus of public debate. Missouri already had more than 10,000 slaves and was poised to join the southern slave states in Congress.

Accordingly, Congressman James Tallmadge of New York proposed an amendment to Missouri’s application for statehood. Tallmadge claimed that the institution of slavery mocked the Declaration of Independence and the liberty it promised to “all men.” He proposed that Congress should admit Missouri as a state only if bringing more slaves to Missouri were prohibited and children born to the slaves there were freed at age twenty-five.

Congressmen like Tallmadge opposed slavery for moral reasons, but they also wanted to maintain a sectional balance of power. Unsurprisingly, the Tallmadge Amendment met with firm resistance from southern politicians. It passed in the House of Representatives due to the support of nearly all the northern congressmen, who had a majority there, but it was quickly defeated in the Senate.

When Congress reconvened in 1820, a senator from Illinois, another new western state, proposed a compromise. Jesse Thomas hoped his offer would not only end the Missouri Crisis but also prevent any future sectional disputes over slavery and statehood. Senator Henry Clay of Kentucky joined in promoting the deal, earning himself the nickname “the Great Compromiser.”

Their bargain, the Missouri Compromise of 1820, contained three parts. First, Congress would admit Missouri as a slave state. Second, Congress would admit Maine (which until now had been a territory of Massachusetts) as a free state, maintaining the balance between the number of free and slave states. Third, the rest of the Louisiana Purchase territory would be divided along the 36°30’ line of latitude—or in other words, along the southern border of Missouri. Slavery would be prohibited in other new states north of this line, but it would be permitted in new states to the south. The compromise passed both houses of Congress, and the Missouri Crisis ended peacefully.

Not everyone, however, felt relieved. The Missouri Crisis made the sectional nature of American politics impossible to ignore. Until now, although the Republicans had been strongest in southern states, there had been many northern Republicans as well. The Missouri Crisis split them almost entirely along sectional lines, suggesting trouble to come.

Worse, the Missouri Crisis demonstrated the volatility of the slavery debate. Many Americans, including seventy-seven-year-old Thomas Jefferson, were alarmed at how readily some Americans spoke of disunion and even civil war over the issue. “This momentous question, like a fire bell in the night, awakened and filled me with terror,” Jefferson wrote. “I considered it at once as the [death] knell of the Union.”

For now, the Missouri Crisis did not result in disunion and civil war as Jefferson and others feared.  But it also failed to settle the issue of slavery’s expansion into new western territories, an issue that would cause worse trouble in years ahead.