That's kind of a misunderstanding of the history of conscription in the United States. The draft had existed since before WW2, and men were continually drafted between wars for military service. The Korean War raised draft quotas drastically, as did the Vietnam War; that said, the majority of service members who deployed to Vietnam were actually volunteers (although many of these volunteered specifically to avoid the draft, since volunteers were better able to avoid dangerous postings via joining branches other than the Marines/Army and by having greater control over their specialty).