The correct answer is the Vietnam War. Many male citizens felt it was extremely unfair that they could be drafted into the military at the age of 18 but could not vote until they were 21. This was the case during the Vietnam War, as millions of men under the age of 21 were drafted. These men felt that if they had the ability to vote, they would have more power in persuading their elected officials to get out of this war as a whole. The 26th amendment, after much protest, is implemented as of 1971. This makes the voting age 18 years old all over the United States.