Guido Tabellini notes that Democracy Comes Second:
Countries that become democracies do not, on average, achieve faster economic growth after their political transition; and, vice versa, democracies that fail and relapse into autocracy do not, on average, do worse than before.The positive correlation between income and democracy that one sees across countries could be due to reverse causation: democracy is more likely to persist as a country grows richer. It could also be due to special historical or cultural circumstances: some societies are just more successful than others, both in terms of economic development and with regard to their ability to develop and maintain democratic political institutions.