2 Chronicles 18:1

Now Jehoshaphat had riches and honour in abundance, and joined affinity with Ahab.

The joining in affinity with Ahab came at the time when Jehoshaphat had riches and honour in abundance. That prosperity gave him great influence for truth and righteousness. The affinity was a family alliance formed by his consent to the marriage of his son Jehoram to Athaliah.

She was Athaliah the daughter of Ahab, the daughter of Ahab and Jezebel. By this marriage Judah and Israel were joined together. That union between Judah and Israel was not in God's order. It drew Jehoshaphat into joining Ahab in war against Syria. It later brought disaster upon Jehoshaphat himself and upon many of his people.