The legal justification for Europeans conquering America

This is an interesting passage in a book on American history that goes into the actual thought at the time, or legal justification, for the European taking of lands away from the native Americans. It's not usually thought that there was any legal thought going on about it vis-a-vis the native inhabitants. The relations between the settlers or colonists or traders and their home country, yes; but not the conquerors vs. conquered. That just seemed to be chalked up to the ways of the world. Here it is:

What of lands already occupied, for instance by Native Americans? That question inspired the fourth spirit of English colonization, the racial and legal one. It held simply that the rights of savage or indigent peoples were forfeit. The English first applied that principle in Ireland, the colonial laboratory where they learned contempt and fear for uncivilized neighbors and asserted eminent domain over unimproved lands. John Locke justified that right in his Second Treatise of Government in 1689. He began by asserting, “In the beginning all the world was America,” by which he meant undeveloped, and ended by asserting that American Indians “exercise very little Dominion, and have but a very moderate sovereignty.” In short, the English believed the displacement of indolent people by dynamic civilizers was not only inevitable but just.

That's from Throes of Democracy by Walter A. McDougall.