"[J]ust 100 cities account for 30 percent of the world's economy, and almost all its innovation. Many are world capitals that have evolved and adapted through centuries of dominance: London, New York, Paris. New York City's economy alone is larger than 46 of sub-Saharan Africa's economies combined. Hong Kong receives more tourists annually than all of India. These cities are the engines of globalization, and their enduring vibrancy lies in money, knowledge, and stability. They are today's true Global Cities.
At the same time, a new category of megacities is emerging around the world, dwarfing anything that has come before. A massive influx of people has not only spurred the growth of existing cities, but created new ones virtually from scratch on a scale not previously imagined, from the factory towns in China's Guangdong province to the artificial 'knowledge cities' rising in the Arabian desert. The defining feature of this new urban age will be megalopolises whose populations are measured in the tens of millions, with jagged skylines that stretch as far as the eye can see."
Khanna suggests that to truly understand the world today and where it's heading, one must look back more than a thousand years to the age of citystates.