Final answer:
Before World War II, the Great Depression was the main concern for Americans, fostering isolationist policies. The rise of Adolf Hitler and international conflicts began to change public opinion, culminating in the U.S. joining the war after Pearl Harbor.
Step-by-step explanation:
Prior to the United States entering World War II, the biggest concern for most Americans was the effect of the Great Depression, which led to an isolationist policy aimed at keeping America out of foreign conflicts. The domestic economic challenges posed by high unemployment rates, bank closures, and stock market crashes overshadowed foreign affairs. However, Adolf Hitler's rise to power and the growing aggressions in Europe and Asia began shifting the American perspective, leading up to the pivotal attack on Pearl Harbor, which finally prompted U.S. involvement in the war. This period marked significant societal changes such as the roles of women and ethnic minorities in the workforce, and attitudes towards racial and gender equality.