The years 1850 to 1880 witnessed intense social and political strain and profound cultural changes in the United States. The population boomed with Irish and German immigrants, and manufacturings displacement of agriculture as the dominant source of economy made New York and Boston urban economic centers. The majority of literary theorists and critics were living in New England and New York, attracted by the publishing industry. Several different schools of criticism were beginning to develop during this period, including impressionism, aestheticism, critical idealism, critical realism and scholarly historicism -- all are represented in DLB Volume 64. Regardless of their particular styles, critics of this period all tended to agree that literature should be judged at least partly on how it served the greater national purpose and on its truthfulness in representing the moral natures of human beings, as John W. Rathbun and Monica M. Grecu note in the volumes foreword.