World War I (1914–1918) and World War II (1939–1945) were cataclysmic events during the twentieth century. Congress debated new international commitments and chose dramatically new courses in the aftermath of each world war, defining American foreign policy for the rest of the century. Domestically, Congress passed landmark legislation affecting veterans, women, American Indians, and the structure of the federal government. It also investigated “red scares” with controversial results. As Congress faced the challenges of a post-war world—in 1918 and again in 1945—it considered and enacted legislation that would change the lives of millions of Americans.