From the beginning of the Christian era to about 1850, the urban population of the world never exceeded 7 percent. The Industrial Revolution quickly changed that--today 75 percent of people in the U.S. and other developed countries live in cities, according to the United Nations.
As the chart shows, urbanization in the developing countries (such as China and India) and the least developed countries (such as Ethiopia and Bangladesh) has long lagged behind that of the West and Japan. Early in the 20th century probably no more than 5 percent of the population in European colonies clustered in cities. But since then, the proportion in these ex-colonies and the never-colonized nations has increased twice as fast as that of the West. New York City, for instance, took about 150 years to add eight million, but Mexico City added 16 million in just 50 years. Such extraordinary growth has exacerbated the usual problems of development, making it difficult to supply drinking water, sewage disposal, police protection and other amenities. The comparatively slow pace of European urbanization was partly the result of 45 million or so people emigrating to the New World rather than moving to cities.