Both the United States and the Soviet Union drifted apart after the Russian Revolution of 1917, the Russian Civil War and the Paris Peace Conference. Diplomatic and extensive trading relationships were established under Roosevelt, but relations soured following the Soviet occupation of the Baltic States and eastern Poland. After Hitler broke the Molotov–Ribbentrop Pact the Western powers worked closely with the Soviet Union during the Second World War. Distrust reemerged as Stalin's plans for placing Eastern Europe in the Soviet Union's sphere of influence became apparent towards the war's end, and came to the fore at the Potsdam Conference, just before the atomic bombings of Hiroshima and Nagasaki. Interviewees include George F. Kennan, Zoya Zarubina, Hugh Lunghi and George Elsey.