This text provides an innovative global military history that joins three periods—World War I, the interwar years, and World War II. Jeremy Black offers a comprehensive survey of both wars, comparing continuities and differences. He traces the causes of each war and assesses land, sea, and air warfare as separate dimensions. He argues that the unprecedented nature of the two wars owed much to the demographic and industrial strength of the states involved and their ability and determination to mobilize vast resources. Yet the demands of the world wars also posed major difficulties, not simply in sustaining the struggle but also in conceiving of practical strategies and operational methods in the heat and competition of ever-evolving conflict. In this process, resources, skills, leadership, morale, and alliance cohesion all proved significant. In addition to his military focus, Black considers other key dimensions of the conflicts, especially political and social influences and impacts. He thoroughly integrates the interwar years, tracing the significant continuities between the two world wars. He emphasizes how essential American financial, industrial, agricultural, and energy resources were to the Allies—both before and after the United States entered each war. Bringing the two world wars to life, Black sheds light not only on both as individual conflicts but also on the interwoven relationships between the two.