American Indian Wars: A 700-man Colorado Territory militia attacked a village of Cheyenne and Arapaho, killing 133 men, women, and children.

The American Indian Wars, also known as the American Frontier Wars, and the Indian Wars, was a conflict initially fought by European colonial empires, the United States, and briefly the Confederate States of America and Republic of Texas against various American Indian tribes in North America. These conflicts occurred from the time of the earliest colonial settlements in the 17th century until the end of the 19th century. The various wars resulted from a wide variety of factors, the most common being the desire of settlers and governments for Indian tribes' lands. The European powers and their colonies enlisted allied Indian tribes to help them conduct warfare against each other's colonial settlements. After the American Revolution, many conflicts were local to specific states or regions and frequently involved disputes over land use; some entailed cycles of violent reprisal.

The Territory of Colorado was an organized incorporated territory of the United States that existed from February 28, 1861, until August 1, 1876, when it was admitted to the Union as the 38th State of Colorado.

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 70 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.