Yalta and Potsdam - the basics

Yalta - February 1945: Germany was not yet defeated, so, although there were tensions about Poland, the big three - Stalin, Roosevelt and Churchill - managed to agree to split Germany into four zones of occupation, and to allow free elections in Eastern European countries. Russia was invited to join the United Nations, and Russia promised to join the war against Japan when Germany was defeated.

Potsdam - July 1945: 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.