Jamieson, Fausset and Brown on 1 Kings 22:2

2. Jehoshaphat the king of Judah came down to the king of Israel--It was singular that a friendly league between the sovereigns of Israel and Judah should, for the first time, have been formed by princes of such opposite characters--the one pious, the other wicked. Neither this league nor the matrimonial alliance by which the union of the royal families was more closely cemented, met the Lord's approval (2Ch 19:2). It led, however, to a visit by Jehoshaphat, whose reception in Samaria was distinguished by the most lavish hospitality (2Ch 18:2). The opportunity of this visit was taken advantage of, to push an object on which Ahab's heart was much set.