To break through, even unto the king of Edom - Either because he thought that the king of Edom would connive at his escape or to take vengeance on him for having deserted his former allies (2 Kings 3:8 note).
Related Commentaries of 2 Kings 3:26
2 Kings 3:26
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 swords, to break through even unto the king of Edom: but they could not.