In the early years of the United States, almost all Americans lived in rural settings. By 1900, however, many Americans had moved to cities, especially in the urban North. A surge in immigration and the emancipation of southern slaves led these groups in particular to settle in northern cities. This is an example of which theme in American history?
A. Egalitarianism
B. Progressivism
C. Changing population trends
D. The expansion of civil rights