This is a quote from Jean-Jacques Rousseau's "The Social Contract", Book IV:
However, when the social tie begins to slacken and the state to weaken, when particular interests begin to make themselves felt and sectional societies begin to exert an influence over the greater society, the common interest becomes corrupted and meets opposition; voting is no longer unanimous; the general will is no longer the will of all; contradictions and disputes arise; and even the best opinion is not allowed to prevail unchallenged.
In the end, when the state, on the brink of ruin, can maintain itself only in an empty and illusory form, when the social bond is broken in every heart, when the meanest interest impudently flaunts the sacred name of the public good, then the general will is silenced: everyone, animated by secret motives, ceases to speak as a citizen any more than as if the state had never existed; and the people enacts in the guise of laws iniquitous decrees which have private interests as their only end.
This was written in 1762 by someone whose writing was a central inspiration to those who founded the American republic. And it is also an excellent description of American politics today.