Being born in a British colony in the early 1700s to British subject parents did in fact mean you were also a British subject. Several were also born in Great Britain proper. They were also nearly all ethnically English or Scottish.
Indeed, most of the founding fathers were British.
Also, the founders were not British. Most of them were second and third generation immigrants.
In addition, I don't think you realize how funny this statement is:
> Ethnic politics had little opportunity to arise in these communities, which were individually mono cultural
I wonder if you can spot the massive gaping hole in this logic. I doubt it.