Military Divisions and units of the United States Army. Military Divisions and their locations throughout the Unites States. The United States Army has changed its organization over three periods: 1911–1917, 1917–1941, and 1941–present. These three periods brought major evolutions of the US Army division structure. In the 1911–1917 period the US Army had its first attempts at modernizing the division. The 1917–1941 era brought the first…