Cities are often centers of agglomeration, places where people gather to collaborate with one another. But this is not the only reason they exist. Sometimes, cities are chiefly centers of consumption, where elites gather to devour resources extracted from the rest of the country. And occasionally, they are something like prisons, where troublesome social groups are concentrated so that the authorities can keep an eye on them. Many premodern cities, like Versailles, Naples, or Imperial Rome, were a little like this. But perhaps the greatest example was Tokugawa Edo. Between 1600 and 1868, Japan was dominated by the Tokugawa family. The Tokugawas had prevailed over their rivals after a series of civil wars, establishing a sort of dictatorship known as the Shogunate. They developed a remarkable social system, crafted to preserve their power, and with it, the peace and social stability of Japan.…