Tyler Cowan links to this bit from Daniel Knowles:
"Africa is urbanising without globalising. Sixty years ago the whole of sub-Saharan Africa had no cities with a population of more than a million people. Now it has dozens.
But unlike the English peasants who moved to factory cities in the 19th century, or Chinese ones in the 20th, the people moving to African cities are not moving to new global metropolises. Africa’s urbanisation is not driven by economic growth. Instead, people are moving to miserable mega-cities, with crumbling infrastructure and corrupt political systems, and which export almost nothing. Two thirds of Africa’s urban population growth is accounted for by slums."