The Selective Service Act of 1917 required all men in the U.S. between the ages of 21 and 30 to register for military service. 24,000.000 men registered for the draft by the end of 1918. 4,800,000 men served in World War I (2,800,000 served active combat). 400,000 African Americans served in segregated units. 15,000 Native Americans served as scouts, messengers, and snipers in non-segregated units.