A number of changes had taken place in the five months since the Yalta Conference which greatly affected the relationships among the leaders . The Soviet Union was occupying Central and Eastern Europe ; the Red Army effectively controlled the Baltic states , Poland , Czechoslovakia , Hungary , Bulgaria , and Romania , and refugees were fleeing from these countries . Stalin had set up a puppet Communist government in Poland , and he insisted that his control of Eastern Europe was a defensive measure against possible future attacks , claiming that it was a legitimate sphere of Soviet influence
Yalta Conference
Yalta Conference
Potsdam Conference