After the Potsdam conference, Germany was split into 4 zones, owned by the UK, USA, France, and Soviet Union. Berlin, located inside the Soviet zone, was also split into 4.
Berlin
In 1948, the UK, USA, and France merged their zones to create the Trizone. They also introduced the Deutschmark - a new currency. This allowed them to quickly restore and boost the economy of West Germany, and their zones in Berlin.
Berlin
The Soviet Union thought it was important to make Germany suffer, so they didn't want supplies entering Berlin, because it was inside East Germany. Therefore, they blocked off all road, rail and canal entrances to Berlin for the Western Allies.
Because of the blockade, the Western Allies attempted to send 4,000 tonnes of supplies into Berlin per day, even through the harshest conditions. The Soviet Union couldn't do anything, as shooting down the planes would result in war.
In May 1949, Stalin lifted the blockade because he felt like it was doing more harm than good. It was damaging the reputation of the Soviet Union, and the Western Allies were easily avoiding it.
These series of events led to the signing of NATO (North Atlantic Treaty Organisation) between the Western Allies, and the signing of the Warsaw Pact between the Eastern Bloc.