| Barnes' Notes on the Bible This refers probably to an early period in Jehoshaphat's reign - about his eighth or his ninth year - when he closed the long series of wars between the two kingdoms by a formal peace, perhaps at once cemented by a marriage between Jehoram and Athaliah (1 Kings 22:2 note).
Gill's Exposition of the Entire BibleAnd Jehoshaphat made peace with the king of Israel. First with Ahab, with whom he contracted an affinity, and joined with him in his expedition to Ramothgilead, and with Ahaziah his successor.
Keil and Delitzsch Biblical Commentary on the Old TestamentHe maintained peace with the king of Israel, i.e., with every one of the Israelitish kings who were contemporaneous with him, viz., Ahab, Ahaziah, and Joram, whereas hitherto the two kingdoms had assumed an attitude of hostility towards each other. Even if this friendly bearing towards Israel was laudable in itself, Jehoshaphat went beyond the bounds of what was allowable, since he formed a marriage alliance with the house of Ahab, by letting his son Joram marry a daughter of Ahab and Jezebel (2 Chronicles 18:1).
Geneva Study BibleAnd Jehoshaphat made peace with the king of Israel.
Wesley's Notes 22:44 Made peace - With Ahab first, and then with his son. This is noted as a blemish in his government, 2Chron 19:2, and proved of most mischievous consequence to his posterity.
Matthew Henry's Concise Commentary22:41-50 Jehoshaphat's reign appears to have been one of the best, both as to piety and prosperity. He pleased God, and God blessed him. | 
