I guess one convenient thing about the US was that even if it was composed of immigrants from all sorts of places it managed to hold a coherent identity (::cough Anglo-Saxon cough::) during its period of overland expansion and then it had the better part of an unexhausted continent with which to build its modern maritime empire. Which was, conveniently, when it began to shift towards a pluralist ideology and

Actually wait. I’ve got ideas for another twelve posts in my head right now, but am I really saying anything other than “Either A or Not A! Therefore A is the common factor! Either X is unified or X is fractured! Therefore X transcends all!

(I mean though once you generalize out beyond a certain point what can you say without saying that?)