The future world order will not be dominated by America or China, India or Brazil. It will be built on cities not states, predicts Parag Khanna, author of the forthcoming "How to Run the World". "The defining feature of this new urban age will be megalopolises whose populations are measured in the tens of millions," he says. And many will pose challenges to the countries that give birth to them as globalization allows major cities to pull away from their home states. "Cities are the real magnets of economies, the innovators of politics, and, increasingly, the drivers of diplomacy."