In 1917 the United States passed the Selective Service Act. This act was the first version of the modern Selective Service System upon which all males 18 and up must register for potential military conscription. Since it’s inception, the selective service system has been utilized for 4 main conflicts. This chart shows the total men drafted in the US by war fought.
World War I was not the first conflict that conscription was utilized. In the American Revolution the federal government did not have the power to conscript men for service. However, the federal government encouraged states to conscript men from their state militias to serve in the Continental Army.
In the Civil War, both the Union and Confederacy also had forms of conscription. In this draft Union men were legally allowed to pay someone to take their place. This left a huge difference between the wealthy who could avoid the draft and the poor who had no such choice. These versions of the draft were extremely unpopular and led to large scale riots.
Total Men Drafted in US by War Fought
Looking to avoid the mistakes of the Civil War draft, the Selective Service Act sought to patch the defects of the previous drafts. This new system expressly forbade the substitutions and purchase of exemptions that made the prior drafts so unpopular. Exemptions could still be made for those who had dependents or worked in essential occupations.
When World War I was completed, the Selective Service Act was allowed to expire. It was not replaced until 1940, upon which the first peacetime draft in US history was enacted. Though the US was not at war, Germany had just overrun France and US leaders foresaw the potential to need a larger military to defend America if needed.
World War II saw the most men drafted of any war. This was the largest of the conflicts and required the most manpower. Though the act expired for a year during the postwar military budget cuts, it was brought back as the need for military manpower in the Cold War was realized.
Following the end of the Vietnam War, the draft was ended, though registration with the Selective Service System remained in case the need ever arose again. The last year a draft was enacted was 1973.
Source: Selective Service System