palestinians didnt have an empire, the islamic caliphates were empires created by arabs in the gulf who settled there, hence why palestinians and the surrounding countries, even the jewish tribes that remained, started speaking arabic instead of hebrew and aramaic. otherwise where did all the levantine arabs come from? how could they all come from areas around palestine?
but empires don’t involve replacing the entire existing population. it doesn’t even logistically make sense, and there was no evidence of a mass migration of arabs at the time. also you still never explained why in the bible and the torah it was acknowledged that ppl already existed and lived in Palestine before Abraham and his followers settled there.