So far, no one has addressed my question as to who actually the indigenous peoples of Europe.
Just reading around on Wikipedia, I found that the "indigenous Peoples" of America's northern plains were not the "Sioux" (Lakota . . whatever). In pre-contact times, the Sioux were a woodland people from the area north of Lake Superior. They were pushed west through violent confrontations with the Chippawa/Ojibway.
I couldn't find who were actually the "indigenous peoples" of the Southern Canadien and Northern American Planes.
DNA research shows that the Navaho peoples of the American Southwest actually migrated there from Athabaskan populations in Canada. They seem to have largely displaced the ancient Puebloan people in what is now Arizona, New Mexico and Colorado.