If economic growth relies upon the extent-of-the-market, then openness will decrease the connection between initial income and later growth. Alternatively, learning-by-doing models suggest that wealth will be more positively correlated with growth in open economies, because trade causes advanced economies to specialize in products with more opportunities for learning. We examine twentieth century less developed countries and nineteenth century U. S. states. In both data sets, there is a much stronger correlation between growth and initial wealth among closed economies. These findings support the importance of the extent-of-the-market, and aggregate demand in fostering growth.

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.