Despite increasing political polarization, evidence suggests that most Americans fundamentally agree about basic ideals. So why is political compromise so hard? After all, the nation’s founders were exemplary compromisers, even over slavery, the nation’s most divisive issue. They made necessary, even “great,” concessions over slavery that preserved the Union, and helped hasten slavery’s demise.[time-brightcove not-tgx=”true”]The issue is that political divisions today are not merely over policy preferences, but what American democracy really means, and who it includes. Political compromise in the United States has a history that forces us to confront a deeper question: can people who oppose an unjust, undemocratic status quo actually “compromise” with those who reject democracy for all?One of the most important chapters in this history is what historians call the “Missouri Crisis.” Between 1819 and 1821, debates over Missouri’s admission to the Union consumed Congress. At issue was not simply Missouri’s fate, but the fate of slavery in the expanding United States. The history of the Missouri Crisis demonstrates the consequences of attempting to compromise on basic principles of democracy. Doing so did not lead to the amicable consensus the compromisers hoped for. Instead, it emboldened those who would reject democracy to build their own power, and conditioned them to expect future capitulation to their demands. In 1819, the United States had 22 states, split evenly between those that allowed slavery and those that did not. Then, Missouri petitioned for statehood. To ensure that slave states didn’t outnumber free states, Congressman James Tallmadge Jr. (NY) proposed a measure to bar the further introduction of slavery into Missouri and to free all enslaved people born within Missouri’s borders by the age of 25. Tallmadge’s amendment provoked a bitter two-year argument over Missouri’s admission to the union and over slavery’s place in the young republic.Read More: The Danger of Adjusting State Borders to Reflect Political DividesNorthern “restrictionist” leaders like Tallmadge argued that slavery was immoral and economically inefficient, and that Congress had the power to restrict its expansion into new Western states. “Expansionists”—many in the South, but some in the North, as well—countered by arguing that Congress had no constitutional right to prohibit Missouri’s admission as a slave state. Slavery was not an “evil,” some insisted; it was a “right” that Congress could not touch.Restrictionists and expansionists alike regularly invoked “mutual” “compromise” between North and South as a political ideal. Yet by the Missouri Crisis, Northerners had already lost considerable ground on the issue of slavery. For example, the 1793 Fugitive Slave Act imposed a fine and imprisonment on anyone who helped an enslaved person escape across state lines. Moreover, most Northern antislavery proponents rejected the prospect of racial equality, even though they also despised slavery. This stance weakened their ability to oppose the South’s dominance.This meant the idea of “mutual” compromise strongly favored the slave South. Describing “compromise” as something “each side” had done at the Constitutional Convention of 1787, an anonymous pamphleteer, “A Pennsylvanian,” framed Southerners’ unwillingness to give ground on slavery as a principled political stance that they had “held” onto, “until they carried their point by compromise.” Thus, the idea of “mutual” compromise thinly concealed an insidious double-standard. The expectation for “mutual” compromise rested squarely with slavery’s critics, who were expected to defer to the demands of pro-slavery Southerners. Southerners would use this as a justification to demand greater concessions from anyone critical of slavery.Invoking the ideal of compromise going back to the Constitutional Convention, Southerners argued that they had compromised enough. Alexander Smyth of Virginia argued in January 1820 that Southerners were the ones who had conceded when they agreed to count only three-fifths of the enslaved population. “A concession was indeed made in the convention in proportioning the representatives among the states,” Smyth noted, “but it seems to me that the southern states made it, in agreeing to count only three-fifths of the slaves.” Requiring further compromise, they warned, was an outrageous assault on Southern rights that could provoke Southern violence, and even secession.They backed up their arguments with threats, outbursts, and violent gestures toward their Northern colleagues, often to interrupt their speeches when their arguments veered into criticism Southerners could not stomach.Kentuckian Henry Clay—Speaker of the House and the so-called “great compromiser,” who would broker the Missouri compromise in 1821—interrupted Congressman William Plumer (NH)’s February 1821 speech with what Plumer called “stern tones” and a “repulsive gesture” as a warning “not to obtrude upon him with our New England notions.” Those “notions”—”Liberty, equality, the rights of man”—they were to keep to themselves. Other Southerners invoked the murder of Julius Caesar to make the threats of violence more explicit, warning of “the Ides of March” and to “beware of the fate of Caesar and of Rome.’”Read More: How America Can Still Come TogetherRepeatedly, they told their Northern colleagues who they were. But Northern restrictionists refused to believe them. Daniel Pope Cook of Illinois refused to believe that Virginia would actually “go to war in defence of slavery,” a denial that eerily predicted precisely what Virginia would do 40 years later. “The sober feelings of this nation, and of Virginia in particular, however they may be excited for the moment, will redeem us, I trust, at all times, from such awful calamities,” Cook said.As Cook’s remarks suggest, Northerners found themselves appeasing the fragile emotions of their Southern colleagues, and showing deference in the face of their intimidation. But no matter how much Northern critics conceded, it was never enough.The provisions of the final Missouri compromise seemed to give both restrictionists and expansionists some of what they sought. Expansionists got Missouri admitted as a slave state, with protections enshrined for slavery south of Missouri’s Southern border—the 36°30’ latitude line. Restrictionists got the admission of Maine as a free state and the assurance that states admitted to the Union from the Louisiana Purchase, north of the 36°30’ line, would be free.Yet this compromise absolved slavery’s defenders of any obligation to concede ground, and placed the onus squarely on slavery’s critics to accommodate their demands. These concessions cast a long shadow over antebellum politics thereafter. The South became more emboldened to threaten secession and even violence if their colleagues in Congress challenged them or the institution they sought to protect at all costs.Proslavery leaders could even change the terms of compromise when it no longer suited them. In the 1850s, Democrats—the party of the Slave South—dismantled the Missouri compromise. Congressman Stephen Douglas (D-IL) proposed that new states north of the 36°30’ line be allowed to choose whether they were slave or free based on “popular sovereignty.” “Bleeding Kansas,” a series of deadly conflicts between pro- and anti-slavery settlers in the Kansas territory, later understood as rehearsal for the Civil War, was the result. In 1857, Supreme Court Chief Justice Roger Taney declared the Missouri Compromise itself unconstitutional as part of his infamous Dred Scott decision.Even so, opponents of slavery in the newly-founded Republican Party, led by Abraham Lincoln, initially maintained a willingness to allow slavery where it already existed. Still they sought to compromise with the South to preserve the Union and avoid civil war.Yet it would come anyway. No matter Northerners’ willingness to compromise to preserve the Union, the insatiable demands of Southern slavery meant the Union could survive no more.The Missouri Crisis offers a sobering lesson. Compromising on basic democratic norms like equity, justice, rights for all, and rule of law emboldens those who reject these ideals to demand more and more. The result in the 19th century was not stability or amicability but catastrophe. That lesson has never been more relevant than now.Nathaniel C. Green is Professor of History at Northern Virginia Community College. He is the author of The Man of the People: Political Dissent and the Making of the American Presidency (University Press of Kansas, 2020; paperback, 2024), and is presently at work on a book-length history of the three-fifths clause.Made by History takes readers beyond the headlines with articles written and edited by professional historians. Learn more about Made by History at TIME here. Opinions expressed do not necessarily reflect the views of TIME editors.