Origins of the American Civil War: Militant abolitionist leader John Brown is hanged for his October raid on Harpers Ferry, Virginia (now West Virginia).

The origins of the American Civil War were rooted in the desire of the Southern states to preserve and expand the institution of slavery. Historians in the 21st century overwhelmingly agree on the centrality of slavery in the conflict. They disagree on which aspects were most important, and on the North's reasons for refusing to allow the Southern states to secede. The negationist Lost Cause ideology denies that slavery was the principal cause of the secession, a view disproven by historical evidence, notably some of the seceding states' own secession documents. After leaving the Union, Mississippi issued a declaration stating, "Our position is thoroughly identified with the institution of slavery—the greatest material interest of the world."

In the United States, abolitionism, the movement that sought to end slavery in the country, was active from the colonial era until the American Civil War, the end of which brought about the abolition of American slavery, except as punishment for a crime, through the Thirteenth Amendment to the United States Constitution.

John Brown was an American abolitionist in the decades preceding the Civil War. First reaching national prominence in the 1850s for his radical abolitionism and fighting in Bleeding Kansas, Brown was captured, tried, and executed by the Commonwealth of Virginia for a raid and incitement of a slave rebellion at Harpers Ferry, Virginia, in 1859.

John Brown's raid on Harpers Ferry was an effort by abolitionist John Brown, from October 16 to 18, 1859, to initiate a slave revolt in Southern states by taking over the United States arsenal at Harpers Ferry, Virginia. It has been called the "dress rehearsal" for the American Civil War.