How did events in 1940 lead to the establishment of a draft?

President Roosevelt's signing of the Selective Training and Service Act on September 16, 1940, began the first peacetime draft in the United States. It also reestablished the Selective Service System as an independent agency responsible for identifying young men and facilitating their military service

On September 16, 1940, the United States instituted the Selective Training and Service Act of 1940, which required all men between the ages of 21 and 45 to register for the draft. This was the first peacetime draft in United States' history.

The first peacetime conscription in the United States, the act required all American men between the ages of 21 and 45 to register for the draft. Draftees were selected by national lottery.