 The Cheyenne, Arapaho, and Sioux played the major role in actions that occurred north of the Arkansas River and along the South Platte River, the Great Platte River Road, and the eastern portion of the Overland Trail.The United States government and Colorado Territory authorities participated through the 1st Colorado Cavalry Regiment, often called the Colorado volunteers.The war was centered on the Colorado Eastern Plains, extending eastward into Kansas and Nebraska.