Answer: a Colorado militia on peaceful American Indians.
The Sand Creek massacre is the name of a massacre that occurred on November 29, 1864. The Colorado U. S. Volunteer Cavalry, made up of 675 men, attacked a Cheyenne and Arapaho village. The settlement was peaceful, and two-thirds of those killed were women and children. It is estimated that between 70-500 Native Americans were killed and mutilated.