Towards the end of the war prior to VE day on May 8, 1945, the USG was well-aware that the Soviets were not our friend but a rival. The Soviets behavior in occupying Eastern Europe was evidence of the looming problems. In April 1945 the Soviets established a socialist government in Poland, which violated the Yalta agreement concerning its Declaration on Liberated Europe, especially in the way that it applied to Poland.
And oh BTW, as far as we knew, we were going to need them to help with the final push against Japan...knowledge of the Atomic bomb was held by only a handful of people by VE Day, and even among those who knew of it, there was no perception that it would be a war-ending weapon.
At Yalta, a third agreement was a secret one reached between FDR and Stalin concerning East Asian concessions for the USSR. Port Arthur, Dairen, control of the Manchurian railroads, the Kuriles, and half of Sakhalin Island would go to the Soviet Union, provided they participated in the war against Japan.
During the first weeks of the Truman administration, the question of continued attempts at cooperation with the Soviet Union was raised. As Truman understated, "We were making very little headway with Stalin over the explosive Polish question." The Soviets had formed an interim government consisting mostly of members of the socialist Lublin government in the interest of creating a government friendly to the Soviet Union.
Truman wanted to resolve the issues surrounding the Soviet failure to follow the Declaration on Liberated Europe, but he lacked the talent, experience, and patience to deal with the Soviets at Potsdam in the tradition of Roosevelt. His rhetoric was one of poker analogies, where the leader with the strongest hand would walk away from the conference with the most favorable settlement. Truman’s style was similar to Stalin’s "How many divisions does he have?" approach to post-war settlements. The problem facing Truman in getting Stalin to honor the Yalta protocol was the position of Stalin’s divisions in eastern Europe.
However, Truman and Byrnes saw the atomic bomb and the resulting increase in America’s ability to project force as a substitute for conventional divisions. This was extremely important because domestic American politics would not allow the maintenance of a sizable conventional force in Europe, either to counterbalance Russia or to oversee a defeated Germany.
The importance Truman placed on the bomb in furthering diplomatic goals is evident in the timing of the Potsdam conference. Based on the timetable received from Stimson for the development of the bomb, Truman refused to meet prior to July 15. He cited domestic duties as the reason for not holding the meeting sooner. "It would be extremely difficult for me to be absent from Washington before the end of the fiscal year (June 30)" Churchill urged Truman to agree to meet sooner while Anglo-American conventional forces were still in a strong position, but already the power of the atomic bomb was mitigating calculations of power based solely on conventional forces. As Alperowitz points out, Truman "accepted Berlin as a site for the meeting, and thinking of the latest estimates from Los Alamos, suggested July 15." (From official Atomic Energy Commission history) Indeed, Truman had first been informed of the existence of the Manhattan Project in the context of tensions with Russia over Poland. Stimson was upset by the confrontation between Molotov and Truman, and it compelled him to write to the president on the "political aspects of the S-1 performance" and arrange a meeting to fully brief the president on the Manhattan Project.
The use of the atomic bomb could also have the effect of forcing Japanese surrender before the Soviet declaration of war, or at least before their troops could acquire much Japanese-held territory. After the successful test of the bomb, Byrnes and Truman no longer needed or wished to accept Soviet help in the Far East. They had learned from events in eastern Europe that Soviet assistance came with a price. The State Department warned the President on April 24th that:
Soviet policy will remain a policy aimed at the achievement of maximum power with minimum responsibility and will involve the exertion of pressure in various areas. He [George Kennan] recommends that we study with clinical objectivity the real character and implications of Russian Far East aims."
Although Truman came to accept that if the Soviets received their East Asian concessions would honor the principles of the Open Door, he and Byrnes still wished to forestall Soviet entry if possible. Truman’s desire to prevent Soviet entry is clear in American attempts to stall the negotiations between China and the Soviet Union over the implementation of Soviet control of the concessions. According to Alperowitz, "Byrnes was recorded as saying that ‘he was trying to encourage Soong [T.V. Soong, Chinese Foreign Minister] to prolong the negotiations until after the United States had ended the war.’" It was assumed that the Soviet Union would not begin its offensive until after the China negotiations were completed.
The possibility that the USSR would play sufficiently large a part in Japanese defeat that they would request an occupation zone in Japan was one that bothered the Truman administration. This policy of delaying Soviet entry is overtly stated by Byrnes in numerous sources. Walter Brown recorded in his diary on July 24th that Mr. Byrnes "was still hoping for time [in connection with Chinese-Soviet negotiations], believing after atomic bomb Japan will surrender and Russia will not get in so much on the kill, thereby being in a position to press for claims against China." The entry in James Forrestal’s diaries for July 28th state, "Byrnes said he was most anxious to get the Japanese affair over with before the Russians got in, with particular reference to Port Arthur and Dairen." Byrnes himself wrote in Speaking Frankly in 1947 that "I would have been satisfied had the Russians determined not to enter the war." The developments in Europe were making it clear that the US would only increase its problems by allowing the USSR to have a zone of occupation in Japan.
In those nine years, I rose from third-string book reviewer to senior editor(there are seven of them). I became at last the editor who could do almost anything and was moved at need from one section of the magazine to another. For in time I had edited or written all the departmens except Business. I also became Time'sTime wished to point out how prophetically right its interpretation of foreign news had been in the past, it saw fit to reprint The Ghosts on the Roof, the sad satire I had written on the Yalta Conference the week that it took place ( I did not then know that Alger Hiss was a member of the American delegation).