The theoretical hypothesis: A/B = some people (aka white/black, Muslim/Cristianos, it does not matter)
nomad A came and conquered B settled/nomad (lets say 2000 years ago).
Then B come back and conquered A,
. . . repeat this "process" for 10 times in the next 2100 years.
Now: who has the right to stay (as conqueror) and who must go (if someone will ever welcome them)?
How far in the past we go to "establish" the first come is first served "rights"?
Same problem for conquering the Space/planets:
If some country (more technological advanced, because printing money from their ass to grab the best brains) puts its leg on some planet, before others, the rest of humanity is doomed, or go to war for survival, or what?
How big is the greedy for resources to justify killing others?