The Powder River Expedition of 1865 also known as the Powder River War or Powder River Invasion, was a large and far-flung military operation of the United States Army against the Lakota Sioux, Cheyenne, and Arapaho Indians in Montana Territory and Dakota Territory. Although soldiers destroyed one Arapaho village and established Fort Connor to protect gold miners on the Bozeman Trail, the expedition is considered a failure because it failed to defeat or intimidate the Indians.

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.