This dissertation studies the impact of World War II on the development of the American economy after 1940. Scholars have long-debated the economic consequences of the war, particularly with reference to the macroeconomy and often relying on standard measures of aggregate economic performance. The approach in this dissertation is to study the microeconomic implications of mobilization for World War II. Specifically, the three main chapters address the following questions: What were the human capital costs of the manpower mobilization for young women? Did industrial mobilization promote the growth and diversification of manufacturing in the American South? How much did government spending on supply contracts contribute to migration and the change in the structure of wages between 1940 and 1950? The first chapter provides an overview of America's twentieth century wars and surveys the literature on the impact of World War II. In the second chapter, I find that greater exposure to manpower mobilization decreased young women's educational attainment initially, with important implications for family formation and labor market performance. From the analysis of the third chapter I conclude that the war led to modest reallocation of manufacturing activity toward high value-added sectors, but the war most likely did not create the modern industrial South. In the final chapter I provide evidence that migration induced by World War II played a role in reshaping the structure of wages during the 1940s. Together, the chapters provide important nuance and revisions to our understanding of World War II.