Question

How did the u.s. military recruit the 4 million americans who served during world war 1?

Answer 1

My best guess is the selective service act (s.s.a.)

Answer 2

The system employed in the US for recruitment during WWI was formally denominated Conscription but commonly known as the draft.

President Wilson, in 1917, decided to implement this mechanism in order to reach the 1 million target after the failure of voluntary enlistment that only recruited 73,000 volunteers. In order to optimize the contribution of each person, depending on his personal skills, the The Selective Service Act of 1917 was carefully designed and enacted to achieve so. It turned military service into a liability for all US male citizens, initially those who were between 21 and 31, and later on those between 18 and 45, to enhance the recruitment numbers. It was not possible to be exempted from this military service.