By early December 1941, war had changed much of the world beyond recognition. Nazi Germany occupied most of the European continent, while Japan had turned China into a vast battleground. But these conflicts were not yet inextricably linked, and the United States remained at peace. Scrutinizing five crucial days, Brendan Simms and Charlie Laderman show how Hitler—sometimes perceived as acting impulsively in relation to Pearl Harbor—actually took a calculated risk in provoking America.