The sources and nature of such an identity are complex, and to those who have had little contact with ethnic groups especially in big cities — ethnic identities may be puzzling. They are, however, a widespread element in American society, subject to scrutiny by social scientists and manipulation by politicians. In earlier twentieth-century America, they were of more concern in Eastern cities than in Midwestern farm communities because in rural communities they seemed colorful and accommodative but in cosmopolitan places they were often sources of tension.