Sioux Wars defeated a force of 1,300 Americans under General George Crook. Crook retreated which helped lead to the infamous Battle of Little Big Horn beginning on June 25. Lieutenant Colonel George Custer, commanding a force of over 600 troops, was badly defeated with the loss of over 300 men killed or wounded, including himself. The next major engagement occurred at Slim Buttes on September 9 and 10. While moving toward Deadwood to secure supplies for Crook's command, elements of the 1st Cavalry commander by Capt Anson Mills located and attacked a Sioux village. The Dull Knife Fight, on November 25, and
5th Cavalry Regiment Henry Thomas. The regiment was rebuilt with new officers and recruits loyal to the Union and was assigned to the Army of the Potomac under the command of General George McClellan. On 21 July 1861, the regiment participated in its first battle of the American Civil War, the First Battle of Bull Run; it was the last action in which they would be called the "2nd Cavalry." In the summer of 1861, all regular mounted regiments were re-designated as "cavalry", and being last in seniority among the existing regiments, the regiment was re-designated as the 5th United States Cavalry. During