Deuteronomy 2:9

And the Lord spake to me, saying: Thou shalt not aggrieve the Moabaee, nor make war against them; for I have not given you their land to inherit, because I have given Lachaiath for a possession to the children of Lot.

I have given Ar i.e., the territory of Mo av (most likely it ultimately returned to Mo av after Siḥon conquered it [Numbers 21: 28]).

אל תצר את מואב, “do not harass Moav.” G–d had to warn the Israelites not to harass Amon, Moav and Seir, as they thought that they were legally entitled to inherit the lands of those nations. Seir appears under the heading of Chivvi in numerous places, and it was one of the tribes that G–d had told Avraham in Genesis chapter 15 that his descendants would inherit. This is why the Torah wrote in verse 12 of our chapter that originally the lands occupied at that time were inhabited by a tribe known as Chorim, and that the Edomites, i.e. Seir, had dispossessed the original owners, and did not occupy it legally, so that it was not included in what G–d had spoken about to Avraham in Genesis chapter 15. The ”Chivvi” was not a separate nation among the seventy nations that we read about after G–d destroyed the Tower and mixed up the languages, but a sub-species, such as there were five such among the Midianites, each with a king of their own. Also Ammon and Moav occupied land previously owned by the Re-faim,”(verse 11) so that although the soil was part of what is known to us as “Palestine,” that section was not included in what G–d had promised to Avraham as lands his descendants would inherit in chapter 15. The Moabites themselves had referred to these people as Eymim, i.e. not ethnically part of them. Some of these “names,” were merely acquired names describing how others related to them, i.e. Eymim” are people that inspire Eymah, fear, in those who encounter them. Most of these “nations” were extraordinarily powerful human specimens not only physically but also mentally. This is why they were compared to Anakim, “giants.” G–d did not have to warn the Israelites not to harass the Canaanite tribes who dwelt on their original land, not having engaged in wars of expansion.