During the last fifty years, cities in the developing world have grown tremendously. Changing demographic trends, the persistence of high fertility coupled with declining mortality, have allowed cities of developing countries to maintain high population growth rates in spite of a challenging economic environment.

Nowhere is this dilemma more visible than in the congested cities of sub-Saharan Africa, where projections of urban population growth remain the highest despite the poor economic performance of the countries in that region.

Since 1950, the urban growth rates in SSA are among the highest in the world, it is since 1995 the only region that still has an urban growth rate exceeding 3%.

Such rapid urban population growth raises serous concerns about the ability of African cities to deal economically, environmentally, and politically with such concentrations of people.

The poor economic performance of these countries, when coupled with their strong urban growth, also seems to back the claim that, throughout the history, urbanization played a lesser role in the economic development of the developing world than in that of now developed countries.

Several explanations have been put forward to explain the urban growth spurt in SSA. On the one hand, there are push factors linked to rural population growth, environmental degradation, climate change, and armed civil conflicts.

On the other hand, there are pull factors which are essentially linked to the attraction exerted by higher incomes and productivity, as well as a larger range of available goods and services, in the urban centers on rural migrants.

Productivity improvements and higher incomes may stem from agglomeration economies arising from the diversity of intermediate goods, the matching process in the local labor market, from knowledge spillovers across firms, or any combination of these.

While evidence for agglomeration economies in developed countries and in Asia is fairly well documented, this is not the case for SSA.

Results of the study show the following:

• both unskilled labor mobility and rent-seeking behavior may fuel the formation of large urban centers in developing countries via interregional income shifts and transfers
• even when increasing returns and the freeness of trade are too low for agglomeration to occur in equilibrium in the standard model, special concentration may nevertheless arise because of the  additional purchasing power generated in the capital by either unskilled labor mobility  or tax rates for skilled workers when 
• the rent seeking will always lead to the formation of an elite provided that goods are not too differentiated