Even though Berlin was inside USSR occupied Germany, it was divided between the four allies.$^0$

The cold war was war between communism and capitalism. The rebuilding of Europe is one of the main battleground for this. If the west is able to develop faster and better than the east, it will put on full display the failure of communism.

All of the Eastern Bloc is not allowed to travel to the west. But in Berlin, there is no such barriers. many living in USSR occupied Berlin are going over to western Berlin and seeing the economic prosperity of it. In order to combat this, USSR attempted the blockade the west’s supply routes. In response Britain and US began to fly in supplies. This was called the Berlin air lift. After one year of the blockade, in 1949, the USSR lifted it.

In 1961, the USSR tried a new method. They built the Berlin wall. The USSR closed all crossing points between East and West Berlin. This wall was built to prevent people from escaping the east. The wall fully isolated West Berlin. It finally fell in 1989.$^9$