Russian troops liberated many countries in Eastern Europe from Germany but left Russian troops there. Many people fled as they feared communism. Russia set up Communist government in Poland.
USA had a new President Truman who was more anti-Communist.
USA tested the atom bomb which scared Stalin.
Britain had a new Prime minister Clement Attlee.
Conference dominated by the rivalry between Stalin and Truman.
Stalin and Truman didn't get on well and neither appreciated the others viewpoint.
Problems at Potsdam:
Stalin wanted Germany crippled but Truman didn't want a repeat of the Treaty of Versailles.
Stalin wanted harsh reparations as 20 million Russians had been killed but again Truman didn't want a repeat of the Treaty of Versailles.
As a result of the Sphere of influence, Russia wanted pro-Soviet governments in Eastern Europe but Truman didn't like this idea and adopted a "Get Tough" approach".
The conference ended without complete agreement and both sides were to blame for this.