John Brown’s supporters killed five pro-slavery men at the 1856 Pottawatomie Massacre

Brown concluded that he was on a divine mission to exact revenge after thinking about the sacking of the town of Lawrence by a mob of pro-slavery protesters (May 21, 1856). The Massachusetts senator opposed to slavery, Charles Sumner, was struck with a cane by Representative Preston Brooks on the Senate floor the following day until he passed out. Brooks was a representative from Butler's home state of South Carolina; a few days previously, Sumner had disparaged Democratic senators Stephen Douglas and Andrew Butler in his "Crime Against Kansas" speech.

Five men were pulled out of their homes and killed during a nighttime revenge raid he led on a proslavery hamlet at Pottawatomie Creek in response to those actions.

Newspapers all around the nation condemned the attack—and specifically singled out John Brown. But it didn't stop him: Brown took part in several other battles throughout the area before he finally left Kansas in 1859. Frederick Brown, one of his sons, perished in the conflict. Following this expedition, which came to be known as the Pottawatomie Massacre, local apologists for slavery began to associate "Old Osawatomie Brown" with a dreadful picture.