American history since 1877

  American history since 1877 can be divided in periods of rapid change and intermittent periods of relative calm. Among notable periods of rapid and substantial change, one can identify the Progressive Era (ca. 1880-1920), the New Deal (1933-1945), and the post- World War II years (ca. 1945-1968). Observing politics, economy, diplomacy, society, culture, gender and race alike, which period produced the most substantial change?