12 In earlier times the Horites had lived in Seir, but they were driven out and displaced by the descendants of Esau, just as Israel drove out the people of Canaan when the Lord gave Israel their land.) 13 Moses continued, "Then the Lord said to us, 'Get moving. Cross the Zered Brook.' So we crossed the brook. 14 "Thirty-eight years passed from the time we first left Kadesh-barnea until we finally crossed the Zered Brook! By then, all the men old enough to fight in battle had died in the wilderness, as the Lord had vowed would happen. 15 The Lord struck them down until they had all been eliminated from the community. 16 "When all the men of fighting age had died, 17 the Lord said to me, 18 'Today you will cross the border of Moab at Ar 19 and enter the land of the Ammonites, the descendants of Lot. But do not bother them or start a war with them. I have given the land of Ammon to them as their property, and I will not give you any of their land.'" 20 (That area was once considered the land of the Rephaites, who had lived there, though the Ammonites call them Zamzummites. 21 They were also as strong and numerous and tall as the Anakites. But the Lord destroyed them so the Ammonites could occupy their land. 22 He had done the same for the descendants of Esau who lived in Seir, for he destroyed the Horites so they could settle there in their place. The descendants of Esau live there 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.