The birth of Islam did not cause a whole new race of people to spring from the ground, some of their ancestors lived in the region as well. And according to the Torah the Jewish people who came to that region with Moses during the exodus had to fight off the caananites and philistines before they could settle, so apparently itd been occupied for a while- not that I'd put too much stock in the ancient history thats come down to us, certainly not enough to enforce modern territorial claims