The Ammonites and Moabites rose up against the inhabitants of Mount Seir, devoting them to destruction. And when they had finished off the inhabitants of Seir, they helped to destroy one another.
We have here the foregoing prayer answered and the foregoing promise performed, in the total overthrow of the enemies' forces and the triumph (for so it was rather than a victory) of Jehoshaphat's forces over them. I. Never was army drawn out to the field of battle as Jehoshaphat's was.
Commenting on 2 Chronicles 20:20-30
For the children of Ammon and Moab stood up against the inhabitants of Mount Seir,.... Supposing that they had acted a treacherous part by them, and took on the side of their enemies: utterly to slay and destroy them; as they did: and when they had made an end of the inhabitants of Seir; so that there were none left of them: everyone helped to...
For the children of Ammon and Moab stood up against the inhabitants of mount Seir, utterly to slay and destroy [them]: and when they had made an end of the inhabitants of Seir, every one helped to destroy another. (p) Thus the Lord according to Jehoshaphat's prayer declared his power, when he delivered his by causing their enemies to kill one another.