The Tenth Mounted Legion was levied by Julius Caesar in 61 BC when he was the Governor of Hispania Ulterior. The Tenth was the first legion levied personally by Caesar and was consistently his most trusted.
In the early American Civil War the regular United States Army mounted rifle, dragoon, and two existing cavalry regiments were reorganized and renamed cavalry regiments, of which there were six. Over a hundred other federal and state cavalry regiments were organized, but the infantry played a much larger role in many battles due to its larger numbers, lower cost per rifle fielded, and much easier recruitment. However, cavalry saw a role as part of screening forces and in foraging and scouting. The later phases of the war saw the Federal army developing a truly effective cavalry force fighting as scouts, raiders, and, with repeating rifles, as mounted infantry. Noted cavalry commanders included Confederate general J.E.B. Stuart and on the Union side, Philip Sheridan and George Armstrong Custer.
Post Civil War, as the volunteer armies disbanded, the regular army cavalry regiments increased in number from six to ten, among them Custer's U.S. 7th Cavalry Regiment of Little Bighorn fame, and the African-American U.S. 9th Cavalry Regiment and U.S. 10th Cavalry Regiment. The black units, along with others (both cavalry and infantry), collectively became known as the Buffalo Soldiers. According to Robert M. Utley:
the frontier army was a conventional military force trying to control, by conventional military methods, a people that did not behave like conventional enemies and, indeed, quite often were not enemies at all. This is the most difficult of all military assignments, whether in Africa, Asia, or the American West
The 21st Infantry Regiment ("Gimlet") is a United States Army infantry regiment. The 1st and 3rd Battalions of the 21st currently exist as part of the 25th Infantry Division. The regiment fought in World War II, the Korean War and the Vietnam War, as well as Operation Iraqi Freedom. Task Force Smith, the first American unit to see action in the Korean War, was derived from the regiment's 1st Battalion.