The growth of cities can be extremely important for poverty reduction and the expansion of social services. We know that providing health care and education and even organizing cash transfers is much easier in cities, where government officials are concentrated and civil servants want to live. When cities growth, opportunities to provide services grow as well.
The growth of cities could also contribute to make inequality a more salient political issue. In the cities it is easier to see how others live and to protest against the concentration of income, wealth, infrastructure, etc.
Yet the argument that we are replacing a world of nations with a world of cities seems totally unconvincing. The state still has a national presence and governments are particularly successful when they are able to be present in the whole territory. In fact, the big challenge in the future will be how to link leading geographical spaces and leading sectors with the rest of the economy. And this is a national challenge that can only be successfully met with powerful central administrations.