The leaders of the USA, USSR and Britain had met at Yalta in February 1945 to discuss what action would be taken after World War Two.
Stalin wanted Germany to stay weak. He was concerned that they might attack the USSR again in the future. He wanted them to pay compensation to the USSR for damage during the war.
The USA wanted Germany to stay strong. They wanted to be able to trade with Germany. They believed communism might spread to weak countries.
It was agreed that after Germany's surrender, Germany would be temporarily split into four zones. Britain, the USA, France and the USSR would each control a zone.
Berlin, the capital of Germany, would also be temporarily split into four zones, administered by the same countries. This created a problem for the USA, Britain and France - to reach their zones of Berlin, they had to travel 100 miles into the Soviet zone. There were specifically designated road and rail links for this.
Germany had been defeated, Roosevelt had died and Churchill had lost the 1945 election - so there were open disagreements.
Truman came away angry about the size of reparations and the fact that a communist government was being set up in Poland. Truman did not tell Stalin that he had the atomic bomb.