The U.S. 66th Cavalry Division is a military unit that served within the United States Army during the late 19th and early 20th centuries. Established in 1865, it was one of ten cavalry divisions organized as part of the regular army reorganization after the American Civil War. The division saw action in numerous conflicts, including the Indian Wars, the Spanish-American War, and the Philippine-American War. Throughout its history, the 66th Cavalry Division was composed primarily of mounted troops, though its composition evolved to include motorized and airborne units over time. Notable among its activities were border patrol duties, scouting missions, and participation in large-scale campaigns such as the Battle of Wounded Knee (1890) and the Battle of San Juan Hill (1898). The division was disbanded in 1957.