The act required all men between the ages of 21 and 30 to register for military service. By the end of World War I, around 2.8 million men had been drafted to serve in the military. During the Vietnam War, the Selective Service Act was a subject of great controversy, but the Act was upheld. Currently, the United States requires all men between the ages of 18 and 25 to register with the Selective Service System.