The North and the South managed an uneasy but peaceful coexistence on the issue of slavery for a long time, but as the nineteenth century progressed and the nation began to expand westward, slavery became an increasingly sensitive topic, with Northern abolitionists pushing harder and harder for slavery's elimination. The issue reached the boiling point in 1854, when part of the land acquired in the Louisiana Purchase was divided into two territories, Kansas and Nebraska, along the fortieth parallel. The Kansas-Nebraska Act, written by Illinois Senator Stephen Douglas, who had a vested financial interest in opening up the territory to Chicago-based railroads, all but voided the Missouri Compromise of 1820 and introduced the concept of popular sovereignty — the right of a people organizing as a state to decide by popular vote whether to allow slavery.

Kansas was the first to test the concept, voting overwhelmingly to become a free state. Proslavery advocates, however, refused to accept the popular vote and poured into the territory from nearby slave states such as Missouri in an attempt to shift the balance. In the North, these proslavery troublemakers gave Free State settlers no end of grief. Violence and bloodshed became common as proslavery and antislavery factions battled throughout the Kansas wilderness, earning the region the nickname “Bleeding Kansas.”

More than 200 people died in the vicious guerrilla warfare. In one of the most horrifying acts of mayhem, radical abolitionist John Brown, four of his sons, and two comrades shot and hacked to death five proslavery settlers near Pottawatomie Creek on May 24, 1856, in retaliation for a raid by proslavery forces in the town of Lawrence.