Jamieson, Fausset and Brown on 2 Chronicles 21:6-7

6-7. he walked ... as did the house of Ahab, for he had the daughter of Ahab to wife--The precepts and examples of his excellent father were soon obliterated by his matrimonial alliance with a daughter of the royal house of Israel. Through the influence of Athaliah he abolished the worship of the Lord, and encouraged an introduction of all the corruptions prevalent in the sister kingdom. The divine vengeance was denounced against him, and would have utterly destroyed him and his house, had it not been for a tender regard to the promise made to David (2Sa 7:29; 2Ki 8:19).

2Ch 21:8-17. Edom and Libnah Revolt.