What years was the military draft in effect?

During WWII and Vietnam.

Yes, during WWII and the Vietnam War, but to be more general, the military draft is used whenever the U.S. does not have enough voluntary recruits (meaning, when there are not enough volunteers). So, it could be argued that the military draft is used to "force" people into the army to defend their country. It has not been employed since the early 1970's.