Red Cloud's War (also referred to as the Bozeman War or the Powder River War), an armed conflict between the Lakota and the United States in the Wyoming Territory and the Montana Territory from 1866 to 1868, is fought over control of the Powder River Country in north central Wyoming, which lies along the Bozeman Trail, a primary access route to the Montana gold fields.The war is named after Red Cloud, a prominent chief of Oglala Lakota Sioux who leads the war against the United States following encroachment into the area by the U.S. military.

The war, which ends with the Treaty of Fort Laramie, results in a complete victory for the Lakota and the temporary preservation of their control of the Powder River country.