Which event marked a significant expansion of government bureaucracy in the U.S.?

The event that best marked a significant expansion of government bureaucracy in the U.S. is the Great Depression. During this period, the U.S. government took unprecedented steps to combat widespread economic hardship, leading to the creation of numerous federal agencies and programs. The New Deal, initiated by President Franklin D. Roosevelt, resulted in the establishment of agencies like the Civilian Conservation Corps (CCC) and the Works Progress Administration (WPA). These programs were designed to provide jobs and support for millions of people, effectively increasing the role of the federal government in economic and social welfare.

While other significant events did lead to changes in government structure and responsibilities, none prompted as dramatic an expansion of bureaucracy as the Great Depression. The Civil War, for instance, did lead to increased government involvement in the economy and society, but it was primarily a conflict that influenced direct military and logistical operations rather than a broad expansion of bureaucratic functions. The Industrial Revolution brought about changes in industry and labor, which pushed for regulatory responses, but the respective bureaucratic response was more gradual. The Cold War prompted government growth in areas related to defense and intelligence, yet still did not match the extensive bureaucratic overlay created during the New Deal era due to the Great Depression's direct social needs.