Albert Barnes Commentary Deuteronomy 2:5

"contend not with them; for I will not give you of their land, no, not so much as for the sole of the foot to tread on; because I have given mount Seir unto Esau for a possession." — Deuteronomy 2:5 (ASV)

I have given mount Seir to Esau. Though the descendants of Esau were conquered by David (2 Samuel 8:14), they were not dispossessed of their land, and in the reign of Jehoshaphat they regained their independence (2 Kings 8:20–22).