I once heard something on the History Channel that indicated that the U.S. was unique because of it's make-up of immigrants from around the world. It equated it's free-spirited, conservative, wild-west attitudes with the types of immigrants that came here. In other words, the people that left their homelands, for whatever reason, were the ones who were adventerous, took risks, picked themselves up by their own bootstaps, made their own future, depended on no-one but themselves and their familes and were the ones with "big ideas". Generalization, sure, but I think there's a lot of truth in that. When I think of the things handed down by my immigrant great-grandparents, ideas of self-relience and conservative values, those are hard to change. Now think of this country and the huge number of families that are here because of immigrant forebearers.....kind of make sense. (at least to me).
btw, I've also heard of the impact WWI and WWII has made on European attitudes .... interesting, to say the least.