During the summer of 1864 an Indian war erupted over the plains of Kansas, Nebraska, and the Colorado Territory following the murder of Cheyenne Chief Lean Bear. Lean Bear, a leading peacemaker who had previously met with President Abraham Lincoln in Washington, D.C., was shot from his horse without warning by U.S. troops during a Kansas buffalo hunt. The troops were acting under orders from Colonel John M. Chivington who commanded the military district of Colorado: "Find Indians wherever you can and kill them" (The War of the Rebellion, 1880–1881, pp. 403–404).

In September 1864 the principal chief of the Cheyenne, Black Kettle, and other Cheyenne and Arapaho leaders hazarded a visit to Denver to hold peace talks with Chivington and Governor John Evans. The chiefs were assured that they would be safe from attack if they made the trip to Fort Lyon on the Arkansas River. When Black Kettle arrived there, however, post...