John Brown's Raid on Harpers Ferry 1859 (jan 1, 1859 – jan 1, 0)
John Brown and 21 black and white men went into Harpers Ferry in Virginia with a plan to steal federal arms, spread them to slaves, and start a slave uprising. He held 60 citizens hostage hoping slaves would come forward but none did and 10 of his men were killed. He Himself was captured and hanged for treason.
Northerners respected John Brown but this incident provoked Southerners and mobs of them attacked anyone believed to have antislavery views. It led to the war because it ended most hopes of a compromise between the North and South.
Added to timeline:
Causes of the Civil War