As we saw in Unit 1, cities have existed for thousands of years but grew faster after the industrial revolution. Since the 1950s, rapid urban growth has become a global phenomenon. Given that cities are in different parts of the world, each with its own geography and history, it is difficult to draw universal conclusions about the reasons for city growth. We can make a few general observations. There are exceptions to this general rule.
Population grows when there is a positive rate of natural increase.
This is the main contributor to the growth of cities in developing countries. This was the main contributor to urban growth after industrialization and all the way up to the 1970s. Today, international migration, or the movement of people from one country to another, adds a large number of people to the world's major cities. The city's promises are not always fulfilled. Cities may be known for their bright lights, but not everyone who moves to the city, or is born there, benefits from it.