As thousands of citizens fled East Germany in the early 1960s, Soviet Premier Nikita Khrushchev became irate.Berlin became a particular source of irritation. Khrushchev detested how the German capital was divided into four zones after World War II that the United States, Britain, France, and the Soviet Union oversaw. Related: How a bidding war inspired a WWI veteran to push for an NFL draftCold War tensions became white-hot after the Soviets sh…