The reign of Jehoram over Judah is described in 8:16-24a.
At the age of thirty-two, Jehoram began to reign in the fifth year of Jehoram (Joram) the son of Ahab, king of Israel, while his father Jehoshaphat was king of Judah, and he reigned eight years in Jerusalem (vv. 16-17).
Jehoram married Ahab's daughter and walked in the way of the kings of Israel and as the house of Ahab had done. Although he was king over Judah, he walked in the way of the kings of Israel because he was related to and was influenced by the house of Ahab. Like almost all the kings, he did what was evil in the sight of Jehovah (v. 18).
Verse 19 says, "But Jehovah would not destroy Judah, because of David His servant, as He had promised him that for his sake He would provide a lamp for his children always." This indicates that Jehoram was worthy to be destroyed by God. However, Jehovah was not willing to destroy Judah because He had promised David to provide a lamp for his children.
Formerly, the Edomites did not have a king, but they installed a king over themselves and revolted from under the hand of Judah (v. 20). Jehoram, with all his chariots, fought against Edom, but his people fled to their tents (vv. 21-22a).
Libnah revolted at the same time (v. 22b).
Jehoram died and was buried with his fathers in the city of David (vv. 23-24a).