The Selective Training and Service Act of 1940 was the first peacetime conscription in United States history, requiring men between the ages of 21 and 35 to register for the draft. This act aimed to prepare the U.S. military for potential involvement in World War II, reflecting the growing tensions in Europe and Asia. It marked a significant shift in U.S. military policy, moving from a volunteer-based army to a conscription system as the threat of global conflict loomed.