At the Yalta Conference in 1945, Germany and its capital Berlin were both divided into four zones of occupation.
Berlin lay well inside the Soviet zone of occupation and was a source of tension throughout the Cold War.
This had first become apparent in 1948 with the crisis over the Berlin Blockade.
In the late 1950s, issues around Berlin sparked off one of the biggest of the Cold War crises.
Khrushchev and the East German authorities were concerned about the 'brain drain' from East Germany towards West Germany.
Between 1949 and 1961, an estimated 2.7 million East Germans left for West Germany, and Berlin was the centre of this process as defectors had easy access to its Western sectors.
This created a bad impression of life in East Germany under its hardline communist leader, Walter Ulbricht.
Khrushchev became so troubled with this situation that in November 1958 he gave a speech in Moscow in which he gave the West an ultimatum.
He demanded that, as Berlin lay in East Germany, the Western powers should withdraw their troops from Berlin within six months.
Eisenhower did not want to give in to Khrushchev’s demands, and believed a military presence was necessary to protect West Berlin’s freedom. It was agreed to hold a summit meeting to resolve the ultimatum.
They held a conference in Geneva in May 1959, and then again in September 1959 at the US presidential residence Camp David in the US.
Although no agreement on the long-term fate of Berlin was reached, the ultimatum on Berlin was withdrawn by Khrushchev, and it was agreed that further negotiations would take place in Paris the following year.