What does the promise actually say?
It is a covenant with conditions, not a deed with a border.
Read it and the first thing you notice is that it is not written like a title document. God's grant to Abraham comes attached to obligations, and the same Torah that records the promise spends chapters warning that the land can be lost. Leviticus 26 and Deuteronomy 28 promise exile as the penalty for a nation that behaves badly in it, and the prophets then narrate exactly that happening, twice, in the harshest terms any people has ever written about itself. A propaganda document does not include the clause where you get evicted. Jewish tradition has read the land as held in trust and forfeitable for three thousand years, which is the opposite of "it is ours because a book says so."
Leviticus 26:33 "And I will scatter you among the nations, and I will draw out a sword after you, and your land shall be a desolation."
And note what the same texts have the patriarchs do when they want a specific piece of ground. Abraham does not claim Hebron by divine grant; he buys the cave of Machpelah for four hundred silver shekels, in public, in front of witnesses, and the text records the price (Genesis 23). Jacob buys a plot at Shechem for a hundred pieces of silver (Genesis 33:19). David refuses to accept the threshing floor of Araunah as a gift because "I will not offer to the Lord my God burnt offerings that cost me nothing" (2 Samuel 24:24). Three of the sites most contested today, Hebron, Nablus and the Temple Mount, are the three the tradition insists were purchased and receipted. That instinct did not go away: the Zionist movement bought its land too, acre by acre, at inflated prices, under Ottoman and then British law.