Jews were not the first people in Eretz Yisrael. Hashem gave it to us by directing and empowering Yehoshua ben Nun to drive out the folks who were already there. It does not matter who was there first. It’s ours, when Hashem is ready to return us to it.
As for when the “Palestinians” arrived in Israel, it depends on whether they are descendants of the Caananites or some other people, e.g., Persians, Greeks or New Yorkers.