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Some six weeks after the United States formally entered the First World War, the U.S Congress passes the Selective Service Act on May 18, 1917, giving the U.S. president the power to draft soldiers. ... The act required all men in the U.S. between the ages of 21 and 30 to register for military service.

The Selective Service Act of 1917 or Selective Draft Act authorized the United States federal government to raise a national army for service in World War I through conscription.