Joseph Stalin (representing the USSR) Winston Churchill (representing the United Kingdom) Franklin D. Roosevelt (representing the United States)
At the Tehran Conference, Nov. 28 - Dec. 1, 1943, the western members of the Allies (Roosevelt and Churchill) committed to what Stalin had been seeking for some time: opening a second front of the war with Germany. The USSR had been battling Germany on the Eastern Front since June of 1941. France had been under German control since 1940. To defeat Germany, it was deemed necessary to retake France on the Western Front. Ultimately, this would become the famous "D-Day" invasion of June, 1944.
One argument was that if the U.S. solely did a "test demonstration" of the atomic bomb, versus dropping it immediately on Japan, Japan would see the devastation of the bomb and would surrender on their own will without suffering huge losses.