John F. Kennedy became U.S. president in January 1961. He agreed to meet Khrushchev in June of that year. But shortly before the summit in Vienna, Kennedy's attempted invasion of Castro's Cuba, at the Bay of Pigs, failed miserably. Khrushchev attempted to bully Kennedy at the summit, warning him that Soviet bloc forces could invade West Berlin at any time.

By that time, the flow of refugees from East to West Berlin had become a torrent. East German officials begged Moscow to let them stem the flow. On the morning of August 13, 1961, East German and Soviet troops sealed the East Berlin side of the border, closing crossing points and erecting barricades. Berlin was divided.
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