The "Russian-American war" was the informal name given to a nuclear war that occurred in the 1967 of an alternate visited by Crosstime Traffic. The exact causes were not certain, but the war resulted in a massive nuclear exchange between the United States and the Soviet Union that caused the collapse of civilization. However, the human race did survive in both Russia and America. Survivors also existed in Mexico and Japan, but it was not clear if those countries (or others) engaged in the war and nuclear exchange.
Russian and American survivors both stated that the other country launched the initial attack. Based on research done by Liz Mendoza and her family at UCLA, it was believed that the Soviets launched their missiles first, likely due to the continued presence of hardliners (including Vyacheslav Molotov) in the Soviet government. She theorized that the war might have been caused due to a differing escalation over the Vietnam War or the Six-Day War.