Sforno on Deuteronomy 2:12/ספורנו על דברים ב׳:י״ב

1וישמידום. Esau and Moav destroyed more land and people than they needed for themselves. They did so in order to wipe out all the former people residing there so that they could not one day avenge their defeat. Neither Esau nor Moav populated all the land under their control The area known as Har Seir bordered on areas formerly belonging to Moav and was unpopulated by any members of the tribe of Esau. The same was true on the other side of that boundary; it was not populated by any Moabites. This is why Moses is speaking of G’d having told him that although this was in effect “no-man’s land,” the Israelites were not even to traverse this region, as, nominally, it belonged to either the descendants of Lot or those of Esau.

2כאשר עשה ישראל, a reference to the time when the Torah was committed to writing when the lands of Sichon and Og had already been captured. Those two kings had been most powerful; nonetheless, they had been vanquished within a very short space of time, contrary to accepted norms. This all showed that G’d had given these lands to the Israelites.