Thomas Piketty's Theory of Economic Inequality is A Natural: Wealth Grows Faster Than Incomes

Thomas Piketty, author of  Capital in the Twenty-First Century, makes a major contribution by putting forth a theory of natural economic evolution under capitalism. 

His argument is that capital or wealth grows at the rate of return to capital, a rate that normally exceeds the economic growth rate. Thus, economies will tend to have ever-increasing ratios of wealth to income, barring huge disturbances like wars and depressions. 

Since wealth is highly concentrated, it follows that inequality will tend to increase without bound until a policy change is introduced or some kind of catastrophe interferes with wealth accumulation.

http://www.theatlantic.com/business/archive/2014/05/thomas-piketty-is-right-about-the-past-and-wrong-about-the-future/370994/