The Pottawatomie Massacre occurs during the night of May 24 and the morning of May 25, 1856.
In reaction to the sacking of Lawrence (Kansas) by pro-slavery forces, John Brown and a band of abolitionist settlers (some of them members of the Pottawatomie Rifles) kill five pro-slavery settlers north of Pottawatomie Creek in Franklin County, Kansas.
This is one of the many bloody episodes in Kansas preceding the American Civil War, which come to be known collectively as Bleeding Kansas.