re: Work ethic?
Americans are neither more nor less good workers than anyone else, there isn't any magic spell that goes into effect once you cross a national border, or get residency papers, or are born inside a country.
It might be correct to say that we're more productive because of economic and social conditions, but not just because we're Americans. It implies the rest of the world is lazy. If that were the case, they wouldn't be trying so hard to get work here, and we wouldn't be trying so hard to hire them.
And the Spaniards didn't kill off our Indians, they were too busy killing off theirs.