I realize you're looking at this from an outside perspective, Graybeard, but in this case you really should learn something about how Native Americans/American Indians have been treated in this country - and not even all that long ago.
First point is that the native tribes - which, by the way, are legally separate entities; each and every one of them is referred to as a nation, such as Cherokee Nation, Comanchee Nation, Apache Nation, etc - of this country have been treated execrably by the federal government, which has never been shy about breaking treaties it signed with them, singly or as a group. If the federal government had broken treaties with foreign countries the way that it broke them with the Indian Nations as a group, the United States would be the most despised and least trusted country in the world, far above and beyond how certain recent presidents have managed to damage our image. To put it bluntly, there likely wouldn't have been an image to damage.
There are plenty of other things that the federal government did which I won't go into detail on just now, but a couple things you can look up on your own time are the forced relocations and the Trail of Tears. But one thing that is relevant is the Dawes Severalty Act of 1887, which permitted the federal government to parcel off land owned by the various Indian Nations, held in trust by the United States, as individual homesteads. Much of the 'surplus' land was sold off to outside interests, and the money was used to found schools...which their children were forced to go to, and where they were made over in the image of ideal Americans, even to the point of trying to strip as much of their cultural heritage from them as possible. Graybeard, imagine if the English government decided to take your children away from you, put them in boarding schools, and raised them to be ideal Christians.
By the way, part of the reason for this state of affairs is because around the time the US was founded, it defined the various Indian Nations as "domestic dependent nations", but changed this definition in the Indian Appropriations Act of 1871; instead of making treaties with them, Congress could now interact with them by statute. In addition, the land they lived on was managed by Congress, and thus the various land grabs were legal...at least after the fact. It is a supreme irony that as badly as the federal government treated them, it was often used as a way to try to protect them from the even more abhorrent treatment of the states and individuals citizens.