Nixon’s War Led by Kissinger, Nixon’s security advisor, the Vietnam War came to an end in 1973. Kissinger believed in a theory known as the “Domino Effect,” which assumed that if Vietnam became communist then all the other countries in the Asia Pacific would succumb to communism as well. According to Kissinger, this would occur if the United States left Vietnam. It wasn’t until 7 years later that an agreement was signed. This agreement called for a ceasefire, extraction of American troops, and return of American prisoners. Soon after the war, North Vietnam took over the South.