Adam Clarke on 1 Kings 22:47

There was no king in Edom - It is plain that the compiler of this book lived after the days of Jehoshaphat, in whose time the Edomites revolted; see 2Kgs 8:22. David had conquered the Edomites, and they continued to be governed by deputies, appointed by the kings of Judah, till they recovered their liberty, as above. This note is introduced by the writer to account for Jehoshaphat's building ships at Ezion-geber, which was in the territory of the Edomites, and which showed them to be at that time under the Jewish yoke.