While Jehu was punishing Ahab’s family, he found the leaders of Judah and the sons of Ahaziah’s relatives who served Ahaziah, and Jehu killed them all.
The Aramean army came with only a small group of men, but the Lord handed over to them a very large army from Judah, because the people of Judah had left the Lord, the God of their ancestors. So Joash was punished.