The founders of America were Classic Liberals, Conservatives, which is different then today's Modern or Social Liberals. The most cited European Classic Liberal is John Locke, book Two Treatises of Government published 1689. He established the right to have and own property and natural rights of life and liberty. Other classic liberals include Baron de Montesquieu, Voltaire, Hume, Kant, and Smith that introduced spontaneous order, without direction of the state. His key insight is that because of self-interest no exchange will take place without both parties gaining and society is generally better off.
Rousseau is a the father of Social Liberalism and included in the list of Classic Liberalism. Rousseau believed that man is naturally good, and flourishes when he is free. However, man is corrupted by society and held in chains by this corruption and by social constraints. How an inherently good man could be so easily and thoroughly corrupted was never explained. If man molds like soft clay by social engineers, how can he be naturally good? Contradiction for which neither Rousseau, nor his liberal heirs have explained.
Socialism, Communism, and Fascism are the political products of social liberalism. Democratic socialist try to balance contradictory world view, natural goodness of man and man's easy corruption by society. Democratic socialist look to government programs, leviathan size government, to break the chains that hold down man. However; the leviathan government foster special interest, corrupting society, creating new chains. Democratic socialism is chasing its own tail.
World War I and II, the great depression, and Hitler, Stalin, Mao Zedong, etc. mass murders shocks liberals and their faith in the goodness of man. Is the reason liberal talk radio having to answer listeners that call up fail because if man is not good, shatters the beliefs that government driven society is progressing towards breaking the chain holding man back. They can not control talk radio as they do on TV talk and comedy shows.
Conservatism, Parliamentary Democracy, and Federalism are the political products of Classic liberalism. Far less contradiction of their world view exist. Self-interest driven free market and rule of law has created leviathan government foster special interest, corrupting society. But leviathan size government suppresses spontaneous order, without direction of the state.