Answer: The Soviet Union established a blockade that was meant to keep Western nations from providing supplies and support to West Berlin.
Context:
The Allies of World War II divided Germany into four zones of control after the war -- each zone occupied by one of the Allied nations -- Britain, France, the USA, and the USSR. The same thing was done for the city of Berlin, which was in the Soviet-controlled zone (East Germany). East Berlin was governed under Soviet control, and West Berlin was governed by the western Allies -- Britain, France and the USA. The communist USSR was at odds with their former World War II allies (which were democratic and capitalist). In June, 1948, the Soviets sought to drive the other powers out of West Berlin by blockading all land and waterway routes to the city. But the USA and its partners (Britain and France) would not desert the people of West Berlin, and for over a year they used airplanes to drop supplies into the non-Soviet part of the city. This "Berlin Airlift" effort eventually accounted for over 2 million tons of cargo being delivered to West Berlin by air, and the Soviets eventually gave up the blockade. West Berlin remained independent of Soviet control.
