Pottawatomie Massacre, (May 24–25, 1856), murder of five men from a proslavery settlement on Pottawatomie Creek, Franklin county, Kan., U.S., by an antislavery party led by the abolitionist John Brown and composed largely of men of his family. The victims were associated with the Franklin County Court established by the proslavery territorial government. The incident was one of several that stirred national controversy over Bleeding Kansas and slavery in the U.S. territories during the mid-1850s.