I think foremost the people. There is a huge selection bias... to be an American in a new world takes a passionate kind of person with a lot of do-it-yourself mentality. Then to stand in opposition to Britian... few people would do that. So the ones who were left and fought it out and won (with the help of France) were a very select group. Some of that was genetic and Americans still have some of that bias today, but less and less over time.

I noticed similar (but different) selection bias with New Zealand. Very "can do" attitudes down here. Very willing to help each other. Very self-made. But much more yielding to authority (NZ never had a war of independence).

The scribblings came second. The people came first.