As Hitler prepared for and then carried out his assault on Western Europe in the late 1930s through 1941, the U.S. military was severely undermanned; the army was ranked only 19th worldwide in size. For the most part the American public followed an isolationist line, feeling that Hitler's aggression was a European problem that did not affect the United States.

The Japanese attack on Pearl Harbor in 1941 abruptly ended America's isolation, and the country rapidly prepared for a world war on two fronts. Industries converted seemingly overnight to the production of war material, while government agencies sprang up to oversee the mobilization effort. For the first time, women entered the work force on a large scale; others joined the military services, primarily as nurses or in support roles. The military quickly regained its strength, rising to 8 million members by 1945. Patriotism on the home front was fueled by enthusiastic news reports of American victories. This is the story of the successes and failures of the United States in mobilizing for and at the same time fighting a world war.