The Vietnam War was a military conflict on Earth from 1955 to 1975, fought between by the nation-states of Communist North Vietnam and South Vietnam, and their respective allies. The Vietnam War was part of a larger conflict known as the Cold War between the United States of America and the Soviet Union.
The United States was a key ally of South Vietnam, though the war became highly controversial with the American population over the course of the conflict. Combat eventually spread to other nations of Southeast Asia, and ended with a North Vietnamese victory, creating a single nation of Vietnam. (Historical Accounts)
In 1970, Professor Eugene Eckhart of the Illinois State University of Science and Technology worked with United States Army General Cory in creating an army of cloned human soldiers, without fear or moral reservations, who would be used to decisively win the Vietnam War. This plot was discovered by Aegis agent Gary Seven, who had the clones teleported off Earth, and erased Eckhart and Cory's memories of their project.
Shortly afterwards, Curtis A. Wellborn, a close friend of Seven's assistant Roberta Lincoln, joined the US Army and was sent to Vietnam, where he was subsequently killed in action. In December 2008, Roberta took her granddaughter to see the Vietnam Veterans Memorial in Washington, DC and pointed out Wellborn's name to her. (TOS - Assignment: Earth comic: "My Name Is Legion")