The Sand Creek massacre was a massacre of Cheyenne and Arapaho people by the U.S. Army in the American Indian Wars that occurred on November 29, 1864, when a 675-man force of the Third Colorado Cavalry under the command of U.S. Volunteers Colonel John Chivington attacked and destroyed a village of Cheyenne and Arapaho people in southeastern Colorado Territory, killing and mutilating an estimated 69 to over 600 Native American people. Chivington claimed 500 to 600 warriors were killed. However, most sources estimate around 150 people were killed, 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. The massacre is considered part of a series of events known as the Colorado Wars.

The Cheyenne are an Indigenous people of the Great Plains. Their Cheyenne language belongs to the Algonquian language family. Today, the Cheyenne people are split into two federally recognized nations: the Southern Cheyenne, who are enrolled in the Cheyenne and Arapaho Tribes in Oklahoma, and the Northern Cheyenne, who are enrolled in the Northern Cheyenne Tribe of the Northern Cheyenne Indian Reservation in Montana.