Sforno on Deuteronomy 2:23/ספורנו על דברים ב׳:כ״ג

1והעוים היושבים בחצרים עד עזה, even though the latter belonged to the descendants of Esau or the Philistines with whom Avraham had made a solemn non aggression pact, the Israelites were not now denied the right to conquer these lands. The reason they could do so now was that the Philistines no longer owned the land in question כפתורים היוצאימ מכפתור, the Cretans emigrating from Crete because their island could not contain them all and who were seeking “lebensraum,” had annihilated the Avim and replaced them in that land. When the Israelites conquered the land in which Avimelech used to be king, it already had been lost by Avimelech. [Perhaps the reason that this coastal strip was still known as “the land of the Philistines,” long after the Israelites drove out the Canaanites, is the same as when the Torah referred to the land of the descendants of Ammon as “the land of the Refaim,” (verse 20) the latter having been its original owners.” Ed.]