Can cities solve the biggest problems of the twenty-first century better than nations? Is the city democracy's best hope? In the face of the most perilous challenges of our time--climate change, terrorism, poverty, and trafficking of drugs, guns, and people--the nations of the world seem paralyzed. The problems are too big, too interdependent, too divisive for the nation-state. Is the nation-state, once democracy's best hope, today...