It is tempting to think of the 1920s as a distinct period bordered on one end by World War I (1914–18), the bloody conflict that was supposed to spread democracy across the globe, and on the other by the Great Depression (1929–41), the period of economic downturn and hardship when millions lost their life savings, their jobs, and the sense of security they had once known. Yet the events of the 1920s had their roots in the past, and their influence strayed into the future. The political isolationism (the belief in staying apart from international politics and economics) that dominated the United States in this period, for example, grew out of people's disillusionment with war and desire to keep out of other countries' troubles. On the other hand, the changing role of women that was set in motion during the 1920s would continue to...