What role has industrialization played in urbanization in first and third-world nations? As a result in the role of industrialization is classical or modern urbanization more likely to produce slums? Why?

 According to Davis, what is the principal function of the Third World urban edge? Why does he say this? 

Why did Third World cities and their slums grow so slowly during the first half of the 20th Century? Why did Third World cities and their slums grow so fast during the second half of the 20th Century?