Ben Alpers at the Society for US Intellectual History Blog provides a useful capsule history on American Exceptionalism:
For most of the history of the term – which originally emerged in the 1920s in debates between Lovestoneites and Stalinists over the future course of socialism in the U.S. – “American exceptionalism” was principally used to designate the belief that the U.S. was unlike other countries is some fundamental way. Of course, the word “exceptional” has at least two distinct meanings: 1) unusual and 2) outstanding. And though “American exceptionalism” tended for most of its history to be used in the first sense, that second sense always lurked in the shadows of its usage.
Alpers also notes that the idea of a special American destiny or predicament long pre-existed the introduction of the term, but the main purpose of his post seems to be to concede defeat in his efforts as a history professor to distinguish other exceptionalisms from the version of it adopted by the contemporary American right as a central creedal tenet:
In recent years, however, I’ve noticed the newer sense of “American exceptionalism” creeping into our class discussions and the students’ papers. I’ll try to ask about the changing ways in which people have understood the U.S. to be different from other countries, and my students will answer with a litany of ways in which the U.S. has been awesome (frequently in their own views, occasionally in those of the people we’re reading).
It now seems to me that I’ve lost this terminological battle. For the moment, at least, I think I’m going to remove the term “American exceptionalism” from my syllabus, outlines, essay prompts, and exams. I’ll have to use a few more words to get my meaning across. Rather than write “American exceptionalism,” I’ll write something like “the belief that America is fundamentally unlike other nations.”
In my comment I proposed he consider a distinction between exceptionality and exceptionalism, a distinction that I’ve previously tried to advance in various posts also in relation to neo-imperialism and a somewhat geographically deterministic shaping both of American political culture and of American grand strategy – which I also believe converge in unique (or exceptional) ways for America as world-historical power of our era:
I’ve taken to referring to #1 as “exceptionality” – which can refer to a set of readily identifiable geographical and historical facts taken together – and to reserve #2 for “isms” that tend to be associated with one or another #1.
Belief in American exceptionality always implies belief in some other, relatively more normal historical tendency or predicament, but it also just means that we can treat North America as in many ways, materially and concretely, the globe’s prime developable real estate for the entirety of the modern period up to the present, at least initially without prejudice in regard to the form that that development took or its conceivable moral import. I also believe, however, that it will prove impossible for us, either as Americans or as inhabitants of “the world America made” to avoid attributing values of some type to the facts.
Predictably, many of the fiercest opponents of the type of contemporary rightwing exceptionalism described in the post become or turn out to have been not just philosophically anti-exceptionalist or anti-”American exceptionalism” but “anti-American” exceptionalist. It’s also not surprising that people devoted to the view that a nation is not special, is not admirable, is not chosen for a special fate by God, or perhaps is remarkably evil and dangerous (seat of imperialism, militarism, global capitalism, ecological destruction, genocidal colonialism, etc.) will in normal times have difficulty attaining power and influence, since they are denied or deny themselves the indispensable political resources of good honest demagogy.
Further discussion of this topic, as I have previously stressed, requires a return at some point to philosophy of world history as Hegel understood and explained it, and where the idea of a finally necessary link between exceptionality and an exceptionalism other than vulgar right exceptionalism may receive its best defense. We cannot, or anyway I do not, presume that the political right has the idea entirely wrong.
). Go to our 
America, is an idea, that goes back long before the 13 colonies were
even adopted. William Bradford was the quintessential representative
of this view