2 Kings 3:6-8

King Jehoram went out and numbered all Israel As soon as he was settled in his kingdom, his first business was to raise an army to reduce Moab to obedience, and to engage Jehoshaphat to join him as an ally. And he said, I will go up Jehoshaphat unites with him in this war; because the war was just in itself, and convenient for Jehoshaphat, both in the general, that revolters should be chastised, lest the example should pass into his dominions, and the Edomites be encouraged to revolt from him, as they did from his son; and in particular, that the Moabites should be humbled, who had invaded his land before this time, (2 Chronicles 20:1,) and might do so again if they were not brought low; for which a fair opportunity now offered. He answered, The way through the wilderness of Edom Which Jehoshaphat chose, because he wished to have the assistance of the Edomites, who were his tributaries. And it is probable Moab was but weakly fortified on that side.