Emmanuel Saez and Gabriel Zucman in the Boston Review:
Much has been written about the dramatic increase in income and wealth inequality in the United States over the last four decades. This volume of literature not only warns about the injustice of our current system, but also raises alarm that extreme inequality poses a serious risk to our democracy.
Concern about inequality is at least as old as the United States itself. Writing in 1792 about the necessity and dangers of political parties, James Madison made the connection between excessive wealth and its political influence:
The great object should be to combat the evil: 1. By establishing a political equality among all. 2. By withholding unnecessary opportunities from a few, to increase the inequality of property, by an immoderate, and especially an unmerited, accumulation of riches. 3. By the silent operation of laws, which, without violating the rights of property, reduce extreme wealth towards a state of mediocrity, and raise extreme indigence towards a state of comfort.
Excessive wealth concentration, in Madison’s view, was as poisonous for democracy as war. “In war,” he continued, “the discretionary power of the executive is extended; its influence in dealing out offices, honors, and emoluments is multiplied. . . . The same malignant aspect in republicanism may be traced in the inequality of fortunes.”
Wealth is power. An extreme concentration of wealth means an extreme concentration of power: the power to influence government policy, the power to stifle competition, the power to shape ideology.
More here.