A narrow gap between the protestors and the riot police during a demonstration against the Vietnam War in Washington DC, 21st May 1972. 173 demonstrators were later arrested during a violent confrontation with the police. (Photo by Archive Photos/Getty Images)

Protesters demonstrate against the Vietnam War in Washington, D.C., in May 1972, a visual reflection of the majority view that the war was no longer worth fighting. That loss of will was one of the key contributors to the loss of South Vietnam, contends Vietnam combat veteran and military historian Jerry Morelock. (Archive Photos/Getty Images)