Commercial and industrial development, immigration from Europe, and migration from rural areas led to the rapid growth of cities in the northern United States from 1820 on. Urbanization fueled economic growth but also created social upheaval. Cultural divisions intensified in urban areas where Catholics and Protestants, workers and the well-to-do, immigrants, African Americans, and native-born whites lived side by side. Class dynamics also changed with the development of a clear middle class of shopkeepers, professionals, and clerks. Self-conscious about their status as an emerging class, many middle-class Northerners highlighted their distinctiveness from the classes above and below them.