Powerful forces of social change at the turn of the nineteenth century forced American churches and their members to confront, for the first time, the issue of religious toleration. Christiano analyzes the effects of mass immigration and urbanization on various communities. These upheavals required the established churches to either accept or repel a level of religious diversity unimagined by the architects of American liberty. By examining changes in church membership in the largest urban areas, integrating historical research from a number of disciplines with statistical analyses of the United States Census reports of 1890 and 1906, this cross-disciplinary study provides an empirical assessment of the cultural shifts that laid the foundations for the denominational system that prevails in America today.