Charles Ellicott Commentary 2 Chronicles 20:10

"And now, behold, the children of Ammon and Moab and mount Seir, whom thou wouldest not let Israel invade, when they came out of the land of Egypt, but they turned aside from them, and destroyed them not;" — 2 Chronicles 20:10 (ASV)

And (the children of) Mount Seir. — The Maonites are here so called apparently, and thus identified as an Edomite people. (See on 2 Chronicles 20:1).

Whom thou wouldest not let Israel invade. — See the respective prohibitions (Deuteronomy 2:4; Deuteronomy 2:9; Deuteronomy 2:19). Compare also (Numbers 20:14–21) the king of Edom’s refusal of a passage through his territory (Judges 11:15 and following). These tribes were recognized as the kindred of Israel, as being sons of Esau and sons of Lot. (The Syriac has "mount Gebel," i.e., Gebâl, the name of a tribe living in the northern part of Mount Seir, Psalms 73:8.)