I think it's less that they're taught that the native Americans were peaceful and more that they aren't really taught anything about the history of the native population. It usually starts when European settlers come here.
As an aside; I went to the Smithsonian museum of native Americans or whatever it's called. I was MASSIVELY disappointed that it focused almost solely on post-European settlement. I was really hoping for history and information about the tribes before that. They're fascinating, and it seems a little backhanded to just focus on our impact on them (important obviously, but very dismissive of their long history).
>focused almost solely on post-European settlement
That is because the pre-European natives in North America did not write anything down. The only information we have not from European writers is material remains like arrowheads, pottery and the bones of the animals they butchered.
We can tell a lot about their food sources, trade partners, economics, size of communities and civic centers, (material culture) but not much about politics, religion, folklore and class conflict.
https://en.m.wikipedia.org/wiki/Archaeological_culture
As an aside; I went to the Smithsonian museum of native Americans or whatever it's called. I was MASSIVELY disappointed that it focused almost solely on post-European settlement. I was really hoping for history and information about the tribes before that. They're fascinating, and it seems a little backhanded to just focus on our impact on them (important obviously, but very dismissive of their long history).