Legally speaking it would be difficult to determine exactly which Indians "owned" which land, as property rights and a governing body to divide keep track of them was, I gather, virtually unknown at the time. That doesn't make it right, and of course deliberately introducing diseases to the Indians was demonic. But settlers simply landing on the continental United States and setting up shope was not in and of itself a bad thing. It is also important to remember that many missionaries and evangelist were sent to the Indians by Christian denominations.
I suggest that No. Amer. Indians' sense of "property (land)ownership" was more like not owning but by having designated tribal territory. Early land sales between Indians and Euro settlers undoubtedly were negotiated in terms of mutual misunderstanding of the concept of "land ownership."