Extract the causes of income inequality in the United States mentioned in the text. Separate them with a comma.
The text lists the following as causes of income inequality in the United States: decline of labor unions, globalization, skill-biased technological change, superstars, financialization, immigration of less-educated workers, college premium, automation, public policy, corporatism and corpocracy, female labor force participation, and disproportionate stock ownership in households at higher income and education levels.