December 1, 1969. The United States resumes a lottery system for conscription.

This is, frankly, a bit confusing.

The United States had resumed conscription following World War Two in March 1948.  It had only actually expired in January 1947, showing how a need for manpower in the wake of World War Two caused it to actually continue to exist in spite of a large reduction in force following the end of the war.

After coming back into effect in March 1948 it stayed in existence until 1973, but was then done away with following the end of the Vietnam War. By that time conscription was massively unpopular.  It can't be said to have ever really been "popular", per se, but it didn't meet with real resistance until the Vietnam War.

The resumption of a lottery system for the draft, in which each registrant was assigned a number and the number then drawn at random, was designed to attempt to reduce the unpopularity of conscription at that point in the Vietnam War.  Numerous changes were made to the system during the war including ending a marriage exemption and ultimately curtaining an exemption for graduate students. With the adoption of the lottery system also came a change in age focus so that rather than top of those in the age range being drafted it then focused on those who were 19 years old. The reason for this was that if a person's number wasn't chosen in the lottery as a 19 year old, they were not going to be drafted and could accordingly plan around that.

Because of the way that the draft worked prior to 1969, and even after that date, many men joined the service when faced with the near certainty of being conscripted. As a result, oddly, far more men volunteered for service than who were actually conscripted.  Additionally, the number of men who were volunteers for the service who served in Vietnam outnumbered those who were drafted, with a surprisingly large number of troops who served in the war itself volunteering for service in Vietnam.