James C. Bennett explains how America is different — and alike:
Americans have in many ways been congratulating themselves for the wrong things. The truths of the Declaration were hardly novel or shocking to the Englishmen who read them; rather, they saw them as a Whig five-finger exercise that had been boilerplate since 1688. What was shocking was that the Americans were throwing their own ideals back in their face.
Nor were representative, constitutional government and limitations on state power a novelty to the British; these were considered the very essence of the British constitution. What was shocking was the way the Americans divorced these concepts from the British understanding that they were specific liberties granted to the British alone through usage and tradition, but rather something that belonged to all men as a matter of natural law, and that could be effectively claimed.
The British Union in its narrative (as opposed to its realpolitik considerations) justified itself by a set of claims that were essentially looking backwards — dynastic arguments stemming from the Stuart claim to the thrones of both kingdoms, and the ancient claims asserted by Edward I, looking back to the independent British empire established at the end of the Roman Empire, and beyond that to Celtic myth. Such claims could not be used again by any other people. The American Union could not and would not use such justification. It therefore constructed a forward-looking and universalist narrative, one that has been part and parcel of the American national story every since.
That is the real essence of American exceptionalism. Our uniqueness lies not in a denial of our political and cultural continuity with the rest of the Anglosphere, but rather with the way we took the British (and particularly English) experience, and turned it into a univesalized template.