Charles Ellicott Commentary 1 Kings 22:2

"And it came to pass in the third year, that Jehoshaphat the king of Judah came down to the king of Israel." — 1 Kings 22:2 (ASV)

Jehoshaphat the king of Judah came down.

The fuller account of the Chronicles (2 Chronicles 17:0) notices that the early part of his reign had been marked by a continuance or increase of the prosperity of Asa; but 1 Kings 18:1 adds, in significant connection, he had riches and honour in abundance, and joined affinity with Ahab, so that this prosperity was, at any rate in part, dependent on a change of policy from enmity to alliance, with apparently some measure of dependence, dangerous both spiritually and politically, but probably thought to be a necessity.

The visit of Jehoshaphat (2 Chronicles 18:2) was one of festivity, of which Ahab took advantage.