In the months leading up to the Civil War, fear festered in southern living rooms and legislative chambers. Newspapers reported that the newly elected president, Abraham Lincoln, held a “hatred of the South and its institutions [that would] cause him to use all the power at hand to destroy our country” and that his vice president, Hannibal Hamlin, was not only sympathetic to the plight of black Americans but was himself part black—“what we call,” the editor of one Charleston, South Carolina, paper stated, “a mulatto.” Warnings circulated in pamphlets and the press that an antislavery federal government would inspire a wave of violent slave revolts and then allow the South to burn, rather than stepping in to quell resistance. Texas’s declaration of secession asserted that northern abolitionists had for decades been sending “emissaries” to “bring blood and carnage to our firesides.” Georgia’s insisted that the “avowed purpose” of Republican leaders was to “subvert our society and subject us not only to the loss of our property but the destruction of ourselves, our wives, and our children, and the desolation of our homes [and] our altars.”

These claims were not relegated to the fringes of southern society; they emanated from its center. The most powerful people and institutions in the region voiced and acted upon them as fact. But they were unfounded: conspiracy theories, born of white supremacy and the desire to justify and maintain slavery. Even as they helped shield the antebellum South against the rising abolitionism in the North and in other countries, these theories deepened sectional divisions and made the question of slavery all but impossible to settle peacefully. They helped fuel the deadliest war in the nation’s history. And their violent legacy has lingered across centuries.

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These [slave] uprisings contradicted the narratives that southern slaveholders had constructed. In their telling, slaves were well cared for and content, provided with a better life than they could ever build for themselves in freedom—a life that would give them no good reason to turn on their owners.

To square this defense of slavery with the threat of resistance, southern slaveowners “over time shifted toward a more conspiratorial view,” Matthew J. Clavin, an American- and Atlantic-history professor at the University of Houston, told me. “Slaveowners blamed outsiders. Or they blamed free black people. Or they blamed foreign emissaries from London [for] trying to incite their slaves to rebel.”

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For southerners, the John Brown rebellion “lent credence to that conspiratorial thinking that The abolitionists are coming, that Abolitionists are out to get us, that Abolitionists are encouraging slave revolts,” Clavin said. But Brown’s raid was, in reality, “an absolute anomaly. Very few, if any, abolitionists, black or white, were literally willing to start a slave insurrection themselves.”

And slaveholders knew it. “They overstated the threat from abolitionists,” Clavin said. “They did that on purpose, because it served their intellectual needs”—allowing them to unite the South against a common enemy and to defend the narrative that slaves were docile and content.

At the same time, slaveholders worked to further unite the white South in fear of rebellion by circulating the “diametrically opposed image” of enslaved people as innately violent and dangerous, Manisha Sinha, an American-history professor at the University of Connecticut and the author of The Slave’s Cause: A History of Abolition, told me. The revolutionaries in Haiti, for example, were portrayed not as “freedom fighters, but as barbaric people who descended into completely chaotic violence for violence’s sake,” she said.