2 Chronicles 21:8

In his days the Edomites revolted from under the dominion of Judah, and made themselves a king.

The Edomites revolted. That nation had been made dependent by David, and down to the time of Jehoshaphat was governed by a tributary ruler (1 Kings 22:47; 2 Kings 3:9). But that king having been slain in an insurrection at home, his successor thought to ingratiate himself with his new subjects by raising the flag of independence (Josephus). The attempt was defeated in the first instance by Jehoram, who possessed all the military establishments of his father; but being renewed unexpectedly, the Edomites succeeded in completely emancipating their country from the yoke of Judah (Genesis 27:40). Libnah, which lay on the southern frontier and toward Edom, followed the example of that country.