In international trade theory, countries are often treated as homogenous regions, with no account taken of their internal geography. This column uses evidence from China’s Treaty Port Era to show how domestic trade frictions shape welfare gains from trade. Gains from new technologies that lower trade costs are shared, but the gains are not evenly distributed. Lower trade costs can also mean lower welfare for productivity leaders, who may be replaced by low-cost suppliers from less productive regions as the costs of transport decline.