Albert Barnes Commentary 2 Kings 3:26

"And when the king of Moab saw that the battle was too sore for him, he took with him seven hundred men that drew sword, to break through unto the king of Edom; but they could not." — 2 Kings 3:26 (ASV)

To break through, even to the king of Edom - Either because he thought that the king of Edom would secretly allow his escape or to take vengeance on him for having deserted his former allies (2 Kings 3:8 note).