In this concise account of why America used atomic bombs against Japan in 1945, J. Samuel Walker analyzes the reasons behind President Truman’s most controversial decision. Delineating what was known and not known by American leaders at the time, Walker evaluates the roles of U.S.-Soviet relations and of American domestic politics. In this new edition, Walker takes into account recent scholarship on the topic, including new information on the Japanese decision to surrender. He has also revised the book to place more emphasis on the effect of the Soviet invasion of Manchuria in convincing the emperor and his advisers to quit the war. Rising above an often polemical debate, Walker presents an accessible synthesis of previous work and an important, original contribution to our understanding of the events that ushered in the atomic age. J. Samuel Walker, historian of the U.S. Nuclear Regulatory Commission, has published six other books on the history of American foreign policy and the history of nuclear energy.