What's the definition of sand creek massacre

The Sand Creek Massacre was an atrocity in the Indian Wars that occurred on November 29, 1864, when a 700-man force of Colorado Territory militia attacked and destroyed a peaceful village of Cheyenne and Arapaho encamped in southeastern Colorado Territory, killing and mutilating an estimated 70-163 Indians, about two-thirds of whom were women and children. The location has been designated the Sand Creek Massacre National Historic Site and is administered by the National Park Service.