ABSTRACT
Human mobility, after accelerating in the nineteenth century, expanded even further in the twentieth, and shifted among types. Transnational labor migration reached a peak of three million migrants per year in the early twentieth century, fell to a lower level from the 1930s to the 1960s, and then rebounded from the 1970s. Meanwhile two great wars in the first half of the century and many smaller wars throughout the century caused millions more to flee the battlefields and seek refuge, sometimes in hurriedly constructed camps but preferably in cities. Both labor migration and refugee migration contributed to the third major type of migration of the twentieth century: urbanization. The leading human movements of the twentieth century included the expansion of existing cities, the formation of new cities, the creation of various types of suburbs within reach of the cities, and the creation of new relations with villages. By 1990, virtually half the human population – nearly three billion persons – had come to live in urban agglomerations of more than about 20,000 persons.
