The Cold War/Yalta

In 1945, the leaders of the three allies (the USA, Britain and the USSR) met twice to decide the fate of the Axis countries after the War. The first meeting was at Yalta, near the Crimea, in the USSR, in February, between Roosevelt, Stalin and Churchill. It is important to notice that this was before the War was over. Hence, the subject of the conference was to decide what would would happen once Germany had been defeated, so plans were only in brief. The following things were decided at Yalta:

Redivision of Land in Europe
The allies agreed that post-War Germany would be divided into four zones, and that each of the allies would be given a zone to occupy. The remaining zone, it was agreed, would be given to France. Also, a portion of eastern Germany would be given to Poland, although a portion of eastern Poland would be given to the USSR. This created the "Iron Curtain", splitting Europe in two, and increasing tension between the superpowers.

Free Elections
Stalin also agreed at Yalta that he would allow "free elections" in Soviet-occupied eastern Europe. However, the Soviet Union and the other allies appear to have been working to different definitions of the word "free". The Soviet constitution officially allowed "free elections". However, in the Soviet Union, to quote George Orwell,:

All animals are equal, but some animals are more equal than others.

This definition of "free" was not acceptable to the West, and was the beginning of Cold War tensions between the superpowers. However, they were able to agree that "free" elections would be allowed in Eastern Europe.

Japan
The allies also agreed that, three months after VE Day, the USSR would declare war on Japan. This caused problems, once the Truman Doctrine had been instituted, because the USA was not willing to allow further expansion of Communism into Japan, and hence had to use the atomic bomb on Hiroshima and Nagasaki in order to prevent Soviet involvement in the final stages of the War.

The allies met again at Potsdam, later that year.