Outside of states there is no law - only survival. I would expect stateless people to use force to preserve and increase their resources, and I would of course do so myself in such a situation. I'm not sure if the concept of private ownership exists without a sovereign state to enforce laws. I could "support" or "oppose" either side, but if that's just in terms of emotivism there is no authority to sway with my emotions, and it therefore seems moot (in such a scenario I likely wouldn't ever even consider such things, as such considerations would be inapplicable and meaningless). I could also support or oppose by contributing force, in which case I would be doing so in terms of my own survival, with ethical/legal perspectives/judgement remaining inapplicable. Does that make sense? What do you think?
If it were something completely alien like remote tribes then the property rights concepts would need some bridging, but the Levant has had traditional governments for centuries, so in that case I think the fact that it went through a period of instability does not negate that people, including in living memory had legal documentation and ownership deeds to a valid government. In my view, claims should thus pass to the last legitimate government if the time period has been so short. Again I should make it clear I am speaking independent of the fact of who has more firepower right now, ie the legally just solution would be repelling the invaders.
And if none of the previous legitimate sovereign authorities of that territory are interested to administer its present-day property rights claims? The people of that land are effectively stateless, no?
Again, I should clarify that I am speaking of the justification not the practical reality which is where at present whoever has more firepower will manage to own the place. Even if no previous state is interested in it, it does not just make the land free for all morally and justly. It also applies to the houses of Jews that were stolen at end of WW2, it is recent enough I believe it should be restored and any present owner should be compensated and let out.
As I said the practical reality of who has more firepower is a different issue. It might as well be China who owns that patch of land 50 years from now for all we know.