THE LARGEST MASS SHOOTING IN USA HISTORY HAPPENED December 29, 1890. When 297 Sioux Indians at Wounded Knee Creek on the Pine Ridge Indian Reservation in South Dakota were murdered by federal agents and members of the 7th Cavalry who had come to confiscate their firearms, “for their own safety and protection”. The slaughter began after the majority of the Sioux had peacefully turned in their firearms. The Calvary began shooting, and managed to wipe out the entire camp. 200 of the 297 victims were women and children.