Killing people in your territory has nothing to do with murder or not. And the Nazis did not consider Jews to be their citizens. They considered them a foreign ethnic group. The commies considered all those they killed to be evil criminals and death was the just punishment.
Which means you need another definition than just might makes right for whether something is murder, rape, theft, etc. As just starting a war to gain land is not considered "justifiable" the land is stolen. After all look how many people will yell about the Ukraine and Russia situation.
Legitimacy has to be based on something else than naked force, either previous ownership and being the first, or that it is currently theirs and their people are there, etc.