Again I will cite survival of the fittest. We built up immunity to that which could kill us. US as humans. Not us as different nationalities.
Somehow Darwin evolution theory is good but health science is bad.
My point is that the fact that many native Americans died from contact with diseases that the European's brought with them is to note the importance that it was a fact of life and not a conspiracy. It happened, unfortunate, but it just happened. No group of Europeans set out to make that happen.