[NotSammyHagar]

A lot of that reduction in population was from diseases that weren't in the new world before invasion by Europeans. Not many diseases went the other way, I think syphilis is the only major one I've head of that went from the Americas to Europe. Separate from that the Euros were sure following the path of murdering, genocide, and even after the wars were over the US was sending kids to schools to destroy their knowledge about their own cultures. More recently we started learning about the large graveyards at those schools, and the same thing was happening in Canada.