The chronology of the events leading up to the war starts in October 1962, in the middle of the Cuban Missile Crisis. The Soviet Union has shot down an American civil airplane with the goal of intimidating the United States into abandoning its forces and blockade of Cuba. When the U.S. does not back down, Soviet tank divisions are sent to Cuba and Soviet submarines near Florida.
Tensions mount, the United States issues an ultimatum that the Soviets abandoned the island by 6:00 AM Eastern Daylight Time the next day, or it will be interpreted as an act of war. The Soviets refuse, and the President of the United States, John F. Kennedy puts all U.S. military around the world at DEFCON 2.