As if the land belongs to anyone. I "own" a house but recognize that it is mine until I die. Then it will "belong" to whoever moves in after me. And 50 years from now no one will remember my name. But the house will.
It is not the ssame with countries. I try to imagine what my reaction would be if Japan, for instance, suddenly claimed California as its own based on some document from 976AD. I don't think that I would buy into it peacefully.