Piketty fears that given rising levels of wealth inequality, democracy is doomed. People will not tolerate high levels of inequality forever, and repressing their resistance to an unequal social order will eventually require dispensing with democratic forms. I’m not so sure ... procedural democracy limping on against a background of inequality, disdain and humiliation is not an attractive prospect, but it is already a big part of our present and may be the whole of our future unless egalitarian politics can be revived.

-Piketty, Rousseau and the desire for inequality

Yet the US political system has been under the influence of wealthy elites ever since the American Revolution. In some historical periods it worked primarily for the benefit of the wealthy. In others, it pursued policies that benefited the society as a whole ... unequal societies generally turn a corner once they have passed through a long spell of political instability. Governing elites tire of incessant violence and disorder. They realise that they need to suppress their internal rivalries, and switch to a more co-operative way of governing, if they are to have any hope of preserving the social order.

-History tells us where the wealth gap leads

You may pick two, but no more than two, of the following:

Liberalism
Inequality
Nonpathology

... if severe inequality is going to continue, then there must remain some sizable contingent of people who are socioeconomic losers, who will as a matter of economic necessity become segregated into less-desirable neighborhoods, who will come to form new communities with social identities, which must be pathological for their poverty to be stable.

-Tangles of pathology

Oh and the second link makes the point that when the pendulum swings back to more equality overall, it can still increase inequality between groups. The last link is the one that makes the picture really dark, because it suggests that the only way to end systematic oppression of black people is to either make the US more equal than it's ever been, or find a new group to oppress.