American Heritage dict. (the theory or belief that something, especially a nation, does not conform to a pattern or norm)

Wiktionary, June 26, 2009 (the belief that a particular nation does not conform to an established norm)

Wikipedia, June 26, 2009 (Exceptionalism is the perception that a country, society, institution, movement, or time period is "exceptional" (i.e., unusual or extraordinary) in some way and thus does not conform to normal rules or general principles. Used in this sense, the term reflects a belief formed by lived experience, ideology, perceptual frames, or perspectives influenced by knowledge (or lack thereof) of historical or comparative circumstances.)

Here are entered works on the theory or belief that a specific country or other place does not conform to standard patterns or norms in terms of its origins, institutions, credo, and/or historical evolution.