Most Americans would agree, I think, that America is exceptional, but nailing down exactly why can be a matter of contention. With his typical pellucid prose, George Will provides an exceptionally elegant explanation in his forthcoming book The Conservative Sensibility.
Americans were born exceptionally free from a feudal past, and hence free from an established church and an entrenched aristocracy. This made them exceptionally receptive to intellectual pluralism and exceptionally able to achieve social mobility. America had an exceptional revolution, one that did not attempt to define and deliver happiness, but one that set people free to define and pursue it as they please. Americans codified their Founding doctrines as a natural rights republic in an exceptional Constitution, one that does not say what government must do for them but what government may not do to them. And because the Founding experience was the result of, and affirmed the potency of, human agency, Americans are exceptionally impervious to bleak modern anxieties about human destinies being shaped by vast impersonal forces. America’s central government is exceptionally constructed to limit the discretion of those in power by balancing rival centers of power.
Entire books have been written about the subject. Will nails it in six sentences. He is even more concise when he answers the question, “What does American conservatism seek to conserve?” In three words: “the American Founding.”