Although the atomic bomb was never conceived as a tool to be employed in U.S.-Soviet relations, its very existence would have an unavoidable impact on every aspect of America’s foreign affairs. Truman regarded the Soviet Union as a valued ally in the just-concluded fight against Nazi Germany, but he distrusted it as a totalitarian state and was wary of its postwar plans. His personal diaries and letters reveal hope for a satisfactory postwar relationship but determination not to embark on a policy of unilateral concessions. By mid-summer 1945, although he was already upset by indications that the Soviets intended to impose “friendly” governments in the eastern European states they occupied, Truman still wanted the Soviets to enter the war against Japan. Truman and Byrnes also certainly assumed that the atomic bomb would greatly increase the power and leverage of the United States in world politics and would win the grudging respect of the Soviets. However, it is a giant leap to conclude that the bomb was used primarily as a warning to the Soviet Union rather than as a means to compel Japan’s surrender. At the Potsdam Conference in Germany in mid-July, Truman met with British Prime Minister Winston Churchill (who was succeeded near the end of the conference by Clement Attlee) and Soviet leaderJosef Stalin. From Truman’s perspective, the conference had two purposes: to lay the groundwork for rebuilding postwar Europe and to secure Soviet participation in the war against Japan. On July 16, the day before the conference opened, Truman received word that the first atomic bomb had been successfully tested in the New Mexico desert. He shared the information fully with Churchill (Britain was a partner in the development of the bomb) but simply told Stalin that the United States had created a powerful new weapon. Stalin—who had detailed knowledge of the project through espionage—feigned indifference. He also reaffirmed an earlier pledge to attack Japanese positions in Manchuria no later than mid-August. Truman, apparently uncertain that the bomb alone could compel surrender, was elated. Revisionist historians would later argue that the bomb was used in the hope of securing Japan’s surrender before the Soviet Union could enter the Pacific War.