There was significant American opposition to World Wars I and II. While American antiwar dissent was broader and sharper during World War I, dissent also existed during World War II. Even though antiwar dissent did not alter the conduct or duration of the conflicts, both world wars had a major impact on the American peace movement—and through the peace movement, on American society.

World War I

World War I spawned the modern American peace movement. Led by male business and professional elites and supported by middle-class professionals, the prewar peace movement (respectable, practical, and reformist) sought to resolve conflict through international law, arbitration, and conciliation. By contrast, the modern, post-1914 peace movement, characterized by citizen-peace activists, women's peace organizations, and a progressive reformist impulse, was a more militant grassroots movement that...