Big Three: Churchill, Truman and Stalin meet in Potsdam, Germany in July 1945. Truman informed of successful test of bomb. Big Three demand unconditional surrender from Japanese or new weapon would be used. Some suggest that Truman was warning Stalin if he didn?t follow through with the decisions at Yalta, it could happen to the Soviet Union. potsdam atomic bomb Atomic bomb dropped on these two cities: Hiroshima 80,000 to 100,000 killed Nagasaki 65,000 to 80,000 killed Arguments for use Japanese refused to surrender. It was estimated an invasion similar to D-Day was needed to bring the war to an end. US officials estimated conquest of Japan?s empire would last an additional 18 months to 2 years.