The split between rich and poor is yawning ever wider -- but it's poor countries, not just people, that are really falling behind. Branko Milanovic, a World Bank economist, recently put together data showing that between 1820 and 2002, global GDP per capita increased by more than 10 times -- but so did global inequality. As shown by the Gini coefficient, the most commonly used metric, inequality increased steadily throughout the 19th and early 20th centuries. It plateaued after the 1950s, but inequality between countries -- in particular between the developed West and what came to be known as the Third World -- exploded throughout the 20th century and is now a broad gap. Where should we expect this rich country-poor country split to have the most effect? On migration patterns, Milanovic says, because "inequality is now determined more by where you live than the class you belong to." The best way to change your lot in life, it seems, is to move.