Albert Barnes Commentary 1 Kings 22:41

"And Jehoshaphat the son of Asa began to reign over Judah in the fourth year of Ahab king of Israel." — 1 Kings 22:41 (ASV)

The writer returns to the history of the kingdom of Judah (connect this verse with 1 Kings 15:24), briefly sketching a reign that is described much more fully by the writer of Chronicles (2 Chronicles 17–20). Compare also the marginal references.