In the first month and a half after America entered World War I, only about seven percent of the hoped-for number of young men to volunteer for military service actually did so, according to People's History of the United States. In May 1917, the Selective Service Act of 1917 was enacted, making WWI only the second conflict to require a military draft. Drafts were subsequently enacted for World War II, and the Cold War conflicts of Korea and Vietnam, though since 1973 the country has relied on an all-volunteer military.