It seems safe to say that Capital in the Twenty-First Century, the magnum opus of the French economist Thomas Piketty, will be the most important economics book of the year - and maybe of the decade. Mr. Piketty, arguably the world's leading expert on income and wealth inequality, does more than document the growing concentration of income in the hands of a small economic elite. He also makes a powerful case that we're on the way back to "patrimonial capitalism," in which the commanding heights of the economy are dominated not just by wealth, but also by inherited wealth, in which birth matters more than effort and talent. Six of the 10 wealthiest Americans are already heirs rather than self-made entrepreneurs, and the children of today's economic elite start from a position of immense privilege. As Mr. Piketty notes, "the risk of a drift toward oligarchy is real and gives little reason for optimism." Business income, and income from capital in general, is increasingly concentrated in the hands of a few people. In 1979 the top 1 percent of households accounted for 17 percent of business income; by 2007 the same group was getting 43 percent of business income, and 75 percent of capital gains. Both Koch brothers are numbered among the 10 wealthiest Americans, and so are four Walmart heirs. Great wealth buys great political influence - and not just through campaign contributions. Many conservatives live inside an intellectual bubble of think tanks and captive media that is ultimately financed by a handful of megadonors.