On August 23, 1939 – just before the outbreak of World War II (1939-45) in Europe – the enemies of Nazi Germany and the Soviet Union surprised the world with the signing of the German-Soviet Non-Aggression Pact, in which the two countries agreed not to take military action against each other in order to but with its troops occupying a large part of Germany and Eastern Europe, Stalin was able to effectively ratify the concessions he had won at Kanta and use his advantage over Truman and Churchill (who was replaced by Prime Minister Clement Atlee during the conference). In March 1946, barely a year after the von Yalta Conference, Churchill delivered his famous speech declaring that an „Iron Curtain“ had fallen on Eastern Europe, signalling the definitive end of cooperation between the Soviet Union and its Western allies and the beginning of the Cold War. During the conference, the three leaders coordinated their military strategy against Germany and Japan and made a number of important decisions regarding the post-World War II period. The most notable achievements of the conference focused on the next stages of the war against the Axis powers in Europe and Asia. Roosevelt, Churchill and Stalin discussed the conditions under which the British and Americans finally committed to launch Operation Overlord, an invasion of northern France that was to be carried out in May 1944. The Soviets, who had long urged the Allies to open a second front, agreed to another major offensive on the Eastern Front that would divert German troops from the Allied campaign in northern France. Stalin also agreed in principle that the Soviet Union would declare war on Japan after an Allied victory over Germany. In exchange for a Soviet declaration of war on Japan, Roosevelt acceded to Stalin`s demands for the Kurils and the southern half of Sakhalin, as well as access to the ice-free ports of Dairen (Dalian) and Port Arthur (port of Lüshun) on the Liaodong Peninsula in northern China. However, the exact details of this agreement were not determined until the Kanta Conference in 1945.
When arrangements for the meeting were originally discussed, Stalin and Churchill had invited Roosevelt and asked him to stay with them during the meeting. Roosevelt, however, wanted to avoid the appearance of electing one common rather than another, and decided that it was important to remain in the American legation in order to remain independent.  Roosevelt arrived in Tehran on November 27, 1943 and settled in the American legation. .