The gravity of being the only country to use the atomic bomb posed a lasting challenge for Americans’ self-identity. From the early days of their history, Americans had always thought of themselves as a virtuous nation – a nation called to be a model for the world. As the historian Gordon Wood wrote, the American Revolution “gave us our obsessive concern with our own morality and our messianic sense of purpose in the world.” In the deeply rooted sentiments of American exceptionalism, America was a force for good, a redeeming nation. It was that sense that Roosevelt evoked during the war by calling Americans to a crusade against the evil of fascism and to a reform of the world. It fell to historians, as custodians of the public memory, trained to carefully and critically reconstruct how things happened in the past, to question and subject to scrutiny the prevailing explanation that the participants in the decision had given to justify the decision.