United States Army divisions were square divisions until the beginning of [[World War II]]; reorganization as triangular divisions first occurred in 1940late 1939, lasting through early 1942.<ref name=Maneuver />{{rp|135}} During that war, infantry divisions were typically triangular, with the division controlling three infantry regiments.<ref name=House /> Armored divisions were also triangular, but typically organized into [[combined arms]] "[[combat command]]s" (denoted Combat Command A, Combat Command B, and Combat Command Reserve). After World War II, this structure was retained until the "Pentomic Era" described above. In the 1960s, United States Army divisions were reorganized as triangular divisions, but with the division controlling three combined arms brigades. Combined arms doctrine has all but eliminated regimental purpose, and regiments generally exist only as traditional designations. In the first decade of the 21st century, the United States Army began another reorganization, giving the division four brigades and placing more emphasis on the brigade as the main tactical element, with the division acting more like a corps headquarters, parceling out support units to the brigades.
