In 1910, Crystal Eastman was one of the most conspicuous progressive reformers in America. By the 1920s, her ardent suffragism, insistent anti-militarism, gregarious internationalism, and uncompromising feminism branded her "the most dangerous woman in America" and led to her exile in England. Yet a century later, her legacy in shaping several defining movements of the modern era--labor, feminism, free speech, peace--is unquestioned. A founder...