THE WORLD WARS
As the United States rebuilt in the aftermath of the Civil War, total Army strength grew relatively slowly until the mid 1900s. The World War I era saw the creation of several important Army branches, including the Veterinarian Corps, the Chemical Corps, and the Aviation Section within the Army Signal Corps, the precursor to the Air Force.
World War II led to several more milestones in Army history, including the creation of the Office of Strategic Services, which became the CIA, and Franklin Delano Roosevelt's introduction of the G.I. Bill. Two years after the war, the Army established the Medical Service Corps, later renamed the Army Medical Department (AMEDD).