The Powder River Expedition, or the Powder River War or Powder River Invasion, of 1865, is a large and far-flung military operation of the United States Army against the Sioux, Cheyenne, and Arapaho Indians in what soon becomes the Wyoming and Montana territories.

Although soldiers destroy one Arapaho village and establish Fort Connor to protect travelers on the Bozeman Trail, the expedition is considered a failure because it had failed to defeat the Indians and secure peace in the region.