The Berlin Airlift was the Allied humanitarian mission to supply the population of West Berlin with food and fuel, using transport aircraft, during the postwar period. It was carried out through an air corridor by the American and British government to bypass and overcome the blockade that had been imposed by Joseph Stalin on all ground freight transportation systems (railways, roads, and canals) moving from West Germany to West Berlin, in East Germany. It took place from June 1948 to May 1949, and it is considered as the beginning of the Cold War.
In the Spring of 1948, the Allied nations had proposed the Soviet Union to start negotiations on the monetary and economic status of West Berlin. Stalin rejected any proposal and referendum on the issue as he also insisted that the Soviet currency be the only money of exchange not only in East but also in West Berlin. By then, the United States government had just created and introduced the Deutsche Mark as the new currency for West Germany and West Berlin, which was the main cause of concern for the Soviet Union, for it was considered as an economical and geopolitical move by the USA and the UK against the Soviet occupation of Berlin and East Germany.
As a result of this US government financial move, the Soviet Union decided to impose a blockade on all ground traffic running to West Berlin from West Germany and vice versa. Let us remember that West Berlin lay, as an enclave, within the territory of East Germany. Then the Allied powers, headed by the United States, reacted to this action establishing an air bridge between West Germany and West Berlin, with the transport aircraft taking off from Bonn, Bremen, and Hamburg to supply the German population in the western sector of that city mainly with food and coal. The same cargo planes that had been used to transport weapons and airborne troops during World War II were employed again by the Allies to carry out the Berlin Airlift, which was a humanitarian mission.
Night and day, for more than ten months, the American and British aircraft carried all kind of food, fuel, and medicine for the German families, about two million people, living in the western sector of Berlin. Finally, in May 1949, the Soviet Union publicly declared that it would put an end to the blockade if the the Allied nations terminated the counterblockade they had also established. Thus, an agreement was reached and signed.
Below, a map of Germany during the Berlin Airlift. It shows the occupation zones after WW2 and the city the former capital of the defunct Third Reich, which lay as an enclave in the communist territory. The grayish white area in the east is the territory taken away from Germany to be incorporated as part of Poland.
