In the late 1960s, the military demands of the Vietnam War meant that over 200,000 American men had to be drafted every year. In 1969, the Selective Service System instituted a random drawing of birthdates to decide who would be called. As men were needed, the Selective Service System would call up men according to the order that their birthdates were drawn in the lottery. (Thus, those with a low lottery number knew they were very likely to be drafted. Those with a high lottery number could hope that the military’s manpower needs would be filled before their turn came.)
According to the National Archives, there were about 27 million American men eligible for military service between 1964 and 1973. Of that number, 2,215,000 men were drafted into military service. Around 15 million were granted deferments, mostly for education and some for mental or physical problems.
There were more than 300,000 draft evaders in total, of which 209,517 men illegally resisted the draft while some 100,000 deserted. Among them, around 30,000 emigrated to Canada during 1966-72.
In 1977, on his first day in office, President Jimmy Carter controversially offered a full pardon to any draft dodgers who requested one.