And yet the americans didn't line up germans for the ovens to give them a taste of their own medicine. And the atomic bombs on Japan saved countless more Japanese and American servicemen lives than if an invasion of the Japanese mainland had taken place. And the Japanese readily admit that had they gotten the bomb first, they would've used it on us.
As for the native american genocide by whites. So much of their decline can be laid on communicable diseases that they had no immunity to that yes, were brought over by filthy europeans but other than a few documented instances, there was no widespread effort to wipeout the indians using biological warfare. Atrocities and butchery were committed by both parties but it was the particular savagery shown by some indian tribes from the get go that contributed to sentiment shared by many white settlers that the indian needed to be wiped out. This was unrestricted warfare in most cases and a clash of cultures.
As an American, I'm glad the white man prevailed. Civilization and stuff.
This is an interesting article on the genocide of native americans:
http://historynewsnetwork.org/article/7302