At Potsdam, The Grand Alliance agreed to divide Germany, and its capital Berlin, into four separate occupation zones administered by the Soviet Union, the USA, France and Britain. The division was meant to be temporary, but instead lasted for years.
The Berlin Blockade
The Soviets wanted to take as much material as possible, whilst the Western countries wanted to build up Germany's economy. In Dec 1947, talks between the foreign ministers of the occupying powers broke down and the soviets stormed out
The Berlin Airlift
The USA, Britain, and France combined their zones of Germany to create 'Trizonia'. Although this was never their intention, Germany was now split into two parts, western Trizonia and eastern Soviet-controlled Germany. Stalin saw this as the west ganging up on him.
In June 1948, Stalin decided to shut off the land routes across Soviet-controlled Germany into Berlin. Trizonia in Western Germany would no longer be able to communicate with the capital Berlin, and the people of Berlin would soon run out of food.