Uncle Tom’s Cabin, published on this day in 1852, was technically a work of fiction.

As white abolitionist Harriet Beecher Stowe pointed out in the non-fictional key to her work, however, the world of slavery in her book was actually less horrible than the real world. “Slavery, in some of its workings, is too dreadful for the purposes of art,” she wrote. “A work which should represent it strictly as it is would be a work which cannot be read.”

Her book revolves around the story of Tom, a slave who suffers greatly but is sustained by his Christian faith. Plot points in the book include families being separated by slavery and slaves being hunted and killed. In a pre-war climate where those who argued for the abolition of slavery (many from the North) clashed with those who said slavery was an essential and humane institution (many from the South), her book became massively popular. But its very popularity, in a book that forced whites to empathize with enslaved black characters, prompted some to call its story into question.

Pro-slavery white Southerners argued that Stowe’s story was just that: a story. They argued that its account of slavery was either “wholly false, or at least wildly exaggerated,” according to the University of Virginia’s special website on Stowe’s work. Stowe, whose work of fiction had been sympathetic to white Southerners as well as to slaves, may have been stung by the South’s “shrill rejection of the book,” according to the website.

She published The Key to Uncle Tom’s Cabin in 1853. The book, which is much harsher in tone than her novel, purports to present, in her words, “the original facts and documents upon which the story is founded.” But it’s “a prickly, dense book, with none of the readability of Uncle Tom’s Cabin,” according to the University of Virginia. “It’s also a kind of fiction. Although it claims to be about the sources Stowe consulted while writing the novel, for example, she read many of the works cited here only after the novel was published.”

The book also educated whites, and has been cited as one of the popular instigators of the Civil War. “Stowe’s characters freely debated the causes of slavery, the Fugitive Slave Law, the future of freed people, what an individual could do and racism,” according to the Harriet Beecher Stowe Center.

Stowe, who came from an abolitionist family, wrote Uncle Tom’s Cabin for her own reasons, and from her own perspective, writes biographer Joan D. Hedrick. She wasn’t devoid of racial prejudice and assumptions about correct social order placing her white self at the top, writes Hedrick. But the level of sympathy in her work gives it power, Hedrick writes, and whether she read the exact works that she cites in the Key before or after writing the novel, those works corroborate the facts of her story.

Stowe’s book became a rallying cry for the anti-slavery movement. But to many black people, the characters in Uncle Tom's Cabin were insulting. Stowe’s vision of a passive, religious slave who, although he wanted freedom, didn’t want to rise above whites, is a good example of some of the assumptions white Northerners had about the meaning of black freedom. By the early twentieth century, writes Adena Spingarn for The Root, “Uncle Tom” was on its way to becoming the insult it's known as today.