Comment: There was a draft for WWII and WWI

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In reply to comment: Make all soldiers voluntary. (see in situ)

There was a draft for WWII and WWI

I would assume that if it was not needed they would not have had one.
http://en.wikipedia.org/wiki/Conscription_in_the_United_States

IMHO, if we did not have a draft for WWI, we would not have had a WWII, because neither side had the resources to continue fighting. WWI would have ended in a truce, had it not been for the USA entering that war. Without the WWI draft they would not have had enough volunteers to win.