Intro
At the end of the Second World War, U.S., British, and Soviet military forces divided and occupied Germany. Also divided into occupation zones, Berlin was located far inside Soviet-controlled eastern Germany. 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.
Here is a couple documentaries on Berlin Airlift.