" If everyone were free to migrate from one country to another, wages in rich countries would fall and wages in poor countries would rise, and the world would be a much more equal place. Of course, opposition to lower wages in rich countries is precisely why people are not permitted to migrate at will, and it is why meals and haircuts are so cheap in poor countries. The price of land, like the price of labor, cannot be arbitraged between rich countries and poor countries. Cheap housing in India or Africa cannot be brought up to American prices by simply moving the land across the ocean. The presence of cheap land and cheap labor in poor countries explains why price levels in poor countries are so much lower than in rich countries. The market sets the exchange rate to equalize the prices of steel, gasoline, automobiles, and computers—everything that can be and is part of international trade—but the price level depends on goods and services that cannot be traded. Because those are cheaper in poor places, the poorer the country, the lower are the average prices. "

― Angus Deaton , The Great Escape: Health, Wealth, and the Origins of Inequality