Conscription in the United States, known as "the draft," is a system for enrolling able-bodied men in the military. The draft was ended in 1973, although the Selective Service System resumed registering men aged 18 to 25 for conscription in the event of an emergency in 1980. Historically, there have been several reasons for the draft in the United States.
The main reason for conscription historically has been to increase the size of the military in a short space of time. The first example of this in America was the Civil War, during which both the Union and the Confederacy implemented conscription in order to increase the size of their forces quickly. Conscription was only used in cases where a state could not meet its military quota by using volunteers. Men who were drafted were allowed to pay a substitute to serve for them.
Another reason for the draft is to help the military deal with the intake of new personnel. For instance, with the Second World War looming, the U.S. introduced conscription in 1940. The conscription system was therefore functioning smoothly by the outbreak of war in December 1941. Over 11 million draftees served in the war, alongside approximately 6 million volunteers. Knowledge that they would be drafted probably prevented many more from volunteering, allowing the government to call troops as they were needed.
The ability to expand the military rapidly in times of crisis is related to economic considerations. During peacetime, a large army is a wasteful expense, while it is necessary in time of war. A military draft means that the government can maintain a small, professional force in peacetime which can serve as the core of a larger military should war break out. Doing so prevents the heavy expenditures that can strain government budgets during wartime.
There have been objections raised to the draft as long as it has existed, largely on the grounds that it infringes individual liberty. These were particularly pronounced during the Vietnam War. Opposition to the war was widespread, and the draft was criticized for its unfairness. The U.S. abandoned conscription in 1973 and moved to an all-volunteer army, although the Selective Service System continues to register eligible men in case an emergency should make a draft necessary again.