First, the primary cause of cities becoming so crowded is economic. As a
country develops, its cities become the engines of development, thus jobs are
available in these areas. Frankfurt, Istanbul, Bombay and Sao Paolo are all the
economic centres of their countries. For example, Tokyo was the motor for
Japan’s rapid economic development in the 1960’s and 70’s; as a result, its
population increased rapidly. People moved to Tokyo because they could find
employment and establish economic security for themselves and their families
there.