The term Berlin Crisis is applied primarily to the events of 1961, but the status of the former Berlin national capital became a perpetual source of conflict among the wartime allies when control of the city was divided into four sections of militray control while the countryside surrounding the city all became part of the Soviet sphere. The first attempt by the Soviets to modify the status by force led to the Berlin Airlift of 1948-49.
After almost a year, the Soviets relented and surface transportation was resumed. For the next ten years, German immigrants, often possessing skills needed by the East German economy, crossed the demarcation lines in Berlin and fled to the West, which had been unified in 1949 as the Federal Republic of Germany, replacing the French, American, and British zones of occupation. Although the border was officially closed to visits in 1952, the administration of a border that ran down streets in a city was difficult to enforce. The numbers ran around 100,000 for several years and then began to accelerated in 1960 and particularly 1961.
In November 1958, Premier Khruschev issued an ultimatum to the allies, giving them six months to convert Berlin into a demilitarized, free city. The allies refused and asserted their continued right to free access to the city. In early 1959, Krhruschev agreed to a Four Power Summit to resolve the issues. These were followed by direct talks between Khruschev and Eisenhower at the presidential retreat at Camp David. No actual resolution was achieved, but it was agreed that ultimatums should be avoided and a complete resolution would be sought at a meeting in Paris in May 1960. Unfortunately, the story of the U-2 Spy Plane broke just before the conference and killed its potential.
In June, Khruschev renewed his threat to sign a unilateral agreement with East Germany, which would terminate the special access rights of the Western allies to Berlin. The Western Allies responded that this was not legally possible in a unilateral treaty. While indicating some understanding of the Soviet position and some flexibility on a permanent division, Kennedy also requested a military buildup of men and equipment, and doubled the size of the draft.
After stockpiling materials openly for some time, the Germans began, at midnight between Saturday and Sunday, August 11 and 12, 1961, to construct a wall. By morning, the city was effectively divided. Streets were torn up where the wall ran.
The occupying protocol specified that allied troops were allowed to travel freely through the city. The soviets created difficulties and several critical movements ensued.
At height of the tension, lines of American and Soviet tanks faced each other at short distance across the dividing lines. Both sides had live ammunition and orders to fire if fired upon. Eventually, a slow disengagement of the tanks with neither side appearing to abruptly back down was achieved.
After this date, there was no crisis in Berlin regarding control and the division between East and West became hardened. The Berlin Wall remained until it was torn down by civilians on November 8, 1989. Krhruschev responded