the american state never allowed it's settlers to buy allodial title from the indians, but it didn't see the need to sign treaties or uphold roman imperial precedents the way the british did. it just killed them. stealing land from the indians was not really against the law in the united states the way it was and still is in canada.
in fact, the british crown frequently had to insert itself as a source of law in restricting the activity of british settlers in canada. there are episodes where the british police came down hard on british settlers in northern ontario (at the time called upper canada) and it eventually created the rcmp for the express purpose of protecting the indians from canadian settlers. the british realized that canada was virtually uninhabitable and the only way to protect it from american encroachment was to sign treaties with the indians, so it went well out of it's way to stop canadian settlers from stealing indian lands and aggressively prosecuted canadian settlers when it broke the law. it's a very different history in the canadian prairies than the american ones.
the prairies were eventually settled not by british settlers but by scandinavian and ukrainian settlers, and in some cases by scottish settlers, who didn't behave the same way as the british did, for some reason.
there was a change in mentality after confederation in 1867, which is why british columbia is not under treaty. that change in mentality was towards a more american approach, without abandoning british law. the provincial authorities in british columbia just broke the law.
well, now they're going to have to be held accountable for it.