 Complete the following phrase:  In 1917 the regiment became part of the 2nd Infantry Division, with which it served during World War I, World War II, and the Korean War. Reorganized as a parent regiment during the late 1950s as the United States Army adapted its organization to the Cold War, its 4th Battalion served with the 25th Infantry Division in the Vietnam War. The 9ths 1st, 2nd, and 3rd Battalions served in the 