What was the Berlin Airlift, and why did it happen?
The Berlin Airlift happened in 1949. It was a time when the American and British air forces supplied the city of West Berlin with everything it needed to survive -- everything from food to coal. It all had to be flown in.
The reason it happened is that the Russians had cut off access from the Allied zones of occupation in West Germany to West Berlin, which was in the Russian zone (what became East Germany). So the Allies had to either surrender West Berlin or they had to supply it by air.
The Berlin Airlift refers to the massive program of airlifting supplies of essential goods to West Berliners undertaken from June 1948 to September 1949. This program was undertaken when the Soviet Union blocked all rail, water, and road routes through the Soviet zone to the Western sectors of Berlin. After the World War II, Eastern Part of Berlin was controlled by USSR, while the rest was under control of USA, UK and France. Entire Berlin was located within the East German territory controlled by USSR. It was expected that USSR will permit free access to West Berlin to others. However, in June 1948, they blocked all rail, water, and road routes through East Germany to the Western sectors of Berlin, hoping to drive Western troops out of Berlin. The Berlin Airlift was organized to break this blockade.
At the height of Berlin Airlift project planes landed in West Berlin at the rate of one every one to two minutes. As a result USSR ended the blockade in May 1949, and the airlift stopped in September 1949.