A military draft is a system used by governments to enlist citizens into the armed forces during times of war or national emergency. It typically requires eligible individuals, often based on age and health, to serve in the military for a specified period. The draft can be mandatory, meaning individuals must comply, or voluntary, where people can choose to enlist. In the United States, the draft was most notably used during the Vietnam War and is managed by the Selective Service System. While the draft has not been active since 1973, men aged 18 to 25 are still required to register in case it is reinstated.