12 The Horites also lived in Se'ir formerly, but the sons of Esau dispossessed them, and destroyed them from before them, and settled in their stead; as Israel did to the land of their possession, which the Lord gave to them.) 13 'Now rise up, and go over the brook Zered.' So we went over the brook Zered. 14 And the time from our leaving Ka'desh-bar'nea until we crossed the brook Zered was thirty-eight years, until the entire generation, that is, the men of war, had perished from the camp, as the Lord had sworn to them. 15 For indeed the hand of the Lord was against them, to destroy them from the camp, until they had perished. 16 "So when all the men of war had perished and were dead from among the people, 17 the Lord said to me, 18 'This day you are to pass over the boundary of Moab at Ar; 19 and when you approach the frontier of the sons of Ammon, do not harass them or contend with them, for I will not give you any of the land of the sons of Ammon as a possession, because I have given it to the sons of Lot for a possession.' 20 (That also is known as a land of Reph'aim; Reph'aim formerly lived there, but the Ammonites call them Zamzum'mim, 21 a people great and many, and tall as the Anakim; but the Lord destroyed them before them; and they dispossessed them, and settled in their stead; 22 as he did for the sons of Esau, who live in Se'ir, when he destroyed the Horites before them, and they dispossessed them, and settled in their stead even to this day.
Matthew Henry's Commentary on Deuteronomy 2:12-22
Commentary on Deuteronomy 2:8-23
(Read Deuteronomy 2:8-23)
We have the origin of the Moabites, Edomites, and Ammonites. Moses also gives an instance older than any of these; the Caphtorims drove the Avims out of their country. These revolutions show what uncertain things wordly possessions are. It was so of old, and ever will be so. Families decline, and from them estates are transferred to families that increase; so little continuance is there in these things. This is recorded to encourage the children of Israel. If the providence of God has done this for Moabites and Ammonites, much more would his promise do it for Israel, his peculiar people. Cautions are given not to meddle with Moabites and Ammonites. Even wicked men must not be wronged. God gives and preserves outward blessings to wicked men; these are not the best things, he has better in store for his own children.