How did the conferences cause tensions?

The Yalta conference was described as the highpoint of the alliance. However, at this time the Big 3 were still united by their aim to defeat Nazi Germany.

By July 1945 this had changed. Nazi Germany had been defeated and Hitler was dead. The Red Army had swept through Eastern Europe and into Germany, defeating Berlin in the process. When the allies met outside Berlin at Potsdam tensions began to show.
Key Issues to Revise:
1. Roosevelt's Death - Roosevelt had worked well with Stalin however on his death he was replaced by his vice chancellor Truman who had a deep distrust of the communists and was determined to take a tougher line with Stalin and the USSR.
2. Eastern Europe - Throughout Eastern Europe communists were being positioned into key roles in the governments. This worried Truman. The Western Allies were also unhappy with the land that Stalin had annexed from Poland.
3. Atomic Bomb - Truman decided not to inform Stalin of his intentions to drop the atomic bomb on Japan. The destruction the bomb caused shocked the world. Truman hoped it would shock Stalin and make him more amenable in Europe. This backfired as Stalin was angry that Truman did not inform him. He believed that as Allies Truman should have told him. He took this as a great insult and increased the mistrust and suspicion between the two countries. When the second bomb was dropped the USA won the war against Japan and as a result denied Russia's part in the occupation of Japan.