2 Kings 3:8

And he said, Which way shall we go up? These are the words of Jehoram, who leaves to his ally, the elder monarch, the decision of the line of march. They might have crossed the Jordan to the north of the Dead Sea and so come upon Moab from the north, but they would have had more difficulty then in bringing the king of Edom and his army along with them. The LXX. has -Which way shall Igo up?"

through the wilderness of Edom It would seem from 1 Kings 22:47 (see note there) that the Edomite royal family had come to an end, and that Jehoshaphat claimed the rights over that land which had been held in former times by Solomon. Hence the -deputy" spoken of in that passage as -king of Edom" would be one set up and maintained on his throne by the king of Judah. We can see from this how the way through Edom would be easy and would commend itself to Jehoshaphat.