The Marais des Cygnes massacre (/məˈriː də ˈsiːn/, /ˌmɛr də ˈziːn/, or /məˈreɪ də ˈseɪn/) is considered the last significant act of violence in Bleeding Kansas prior to the outbreak of the American Civil War. On May 19, 1858, approximately 30 men led by Charles Hamilton, a Georgia native and proslavery leader, crossed into the Kansas Territory from Missouri. They arrived at Trading Post, Kansas in the morning and then headed back to Missouri. Along the way they captured 11 Free-Staters, none of whom was armed and, it is said, none of whom had participated in the ongoing violence. Most of the men knew Hamilton and apparently did not realize he meant them harm. These prisoners were led into a defile, where Hamilton ordered the men to shoot. He even shot and fired the first bullet himself. Five men were killed.

• http://en.wikipedia.org/wiki/Marais des Cygnes massacre