Answer:
In 1948, Stalin was upset with the 'occupational zones' (Soviet east zone - US,UK,French west zone) set up in Berlin. He expected that blockading the city from western supplies would cause the western Allies to give Soviet's control of the city. The U.S refused, and the Berlin Airlift ensued, in which allied bombers flew over 600 tons of food a day into Berlin, the Soviets soon saw the blockade wasn't working, and lifted it, after being publicly humiliated over the total failure of the blockade.
