In the first half of the 1940s the productive and imaginative energies of 100 million citizens of the United States were harnessed to a sustained project of global violence under the rubric of “total war” mobilization. This dissertation is a study of American moral sentiments under the pressure of that mobilization, which presented profound challenges to assumptions about permissible and impermissible killing, about the responsibility of individuals for state action in a democracy, and about the appropriate (and inappropriate) ways to experience mediated knowledge of a distant conflict. As Americans worked to reconcile their commitment to the war with day-to-day knowledge of its horrors, a broad range of actors – including military censors and civilian journalists, state officials and publishers, child psychologists and children themselves – articulated a vernacular “realism” which acknowledged the moral ambiguity of firebombing and other extreme forms of violence, yet accepted those acts as ethically tolerable. World War II Americans did not erase or turn a blind eye to their polity’s deep implication in international violence; instead, they found ways to come to terms with it at an affective level. In so doing, they established the foundations for Cold War justifications of lethal force which transcended racial and imperial understandings of force rooted in continental expansion and overseas empire. This dissertation draws on a wide range of published and unpublished records, including underutilized military and civilian censorship records, mass circulation print media, public and private surveys of popular opinion, the correspondence of public figures such as Life magazine publisher Henry Luce, and debates over children’s war play, in order to trace and document a transformation in the moral common sense of violence in the American Century.