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 and pay fines.
The USA wanted Germany to stay strong so they could trade with her.
It was agreed that after Germany's surrender, Germany would be temporarily split into four zones. Britain, the USA, France and Russia each had a zone that they controlled.
Berlin, the capital of Germany, would also be temporarily split into four zones, administered by the same countries. As Berlin is in the east of Germany, this created a problem for the USA, Britain and France - to reach their zones in Berlin they had to travel 100 miles into the Soviet zone.
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.