The word urbanization started appearing in print way back in the 1880s, which says something about the growth of American cities. The expansion of Los Angeles was an early example of uncontrolled urbanization. Urbanization is often seen as a negative trend, with bad effects on quality of life and the environment. But apartments require much less heat than houses, and commuting by mass transit rather than cars can reduce pollution and energy use, and cities offer improved opportunities for jobs (and often for education and housing as well), so city growth doesn't make everyone unhappy.