He volunteered for service as a private in the Union Army at the outbreak of the Civil War.

After commanding the entire cavalry division in the Army of the Tennessee, he was appointed and confirmed a brigadier general in the spring of 1864.

[2] His gallantry in the field caused his further promotion to the rank of brevet major general later in 1864.

After the war, he transferred from the volunteer to the Regular Army as colonel of the 9th U.S. Cavalry Regiment (1866).

He succeeded General Gordon Granger as commander of the District of New Mexico (which included New Mexico Territory) in 1876, negotiated a treaty with the Ute Indians in 1880, and became widely known as an Indian fighter.