I agree with Rhi, Dylan and Bertrand. It hasn't been a case of educational one-upmanship at all, as far as I can see. The plight of the native Americans and Australians (as well as many other indigenous peoples around the world, of course) has been so well documented, that my surprise is equal to that if someone said to me they had never heard of the Pyramids, for example, or that Henry VIII had six wives. Books, films, documentaries, general discussion. Even children's programmes - Bertrand gave the example of Disney's Pocahontas. Yes, of course it has been turned into a sort of fairy-tale romance and sanitised for the younger viewer, and the story resembles very little of the actual facts, but one of the underlying messages is the persecution of the native Americans at the hands of the 'white man'. Children's programmes like Little House on the Prairie (someone further back mentioned Dr Quinn, Medicine Woman - romanticised and sanitised, but again, the underlying message is still there). And my children watched those programmes and read books. Dances with Wolves is a recent one, along with many, many other films. How could anyone claim to not know anything about it? Many US States still bear original NA names - Idaho, Iowa, Nebraska, Dakota, et al. Yukon and Nunavut in Canada. Those who say they'd no idea of the history of America AT ALL - have you never wondered, or heard anyone speak about it. And I'm not for one minute suggesting that someone is stupid for not knowing, I am simply completely and utterly baffled as to the reasons why.
I was making light of my lack of Maths knowledge yesterday evening on this same thread, because I know I am utterly crap at Maths, but thinking about it whilst in bed last night, came to the conclusion that my ignorance in Maths is hardly likely to cause offence or distress to anyone but me. 