A central requirement in the design of a legal system is the protection of law enforcers from coercion by litigants through either violence or bribes. The higher the risk of coercion, the greater the need for protection and control of law enforcers by the state. Such control, however, also makes law enforcers beholden to the state, and politicizes justice. This perspective explains why, starting in the twelfth and thirteenth centuries, the relatively more peaceful England developed trials by independent juries, while the less peaceful France relied on state-employed judges to resolve disputes. It may also explain many differences between common and civil law traditions with respect to both the structure of legal systems and the observed social and economic outcomes.

Using theory, case studies, and cross-country evidence, we investigate the factors behind the concentration of a nation's urban population in a single city. High tariffs, high costs of internal trade, and low levels of international trade increase the degree of concentration. Even more clearly, politics (such as the degree of instability) determines urban primacy. Dictatorships have central cities that are, on average, 50 percent larger than their democratic counterparts. Using information about the timing of city growth, and a series of instruments, we conclude that the predominant causality is from political factors to urban concentration, not from concentration to political change.