Albert Barnes Commentary 2 Kings 11:1

"Now when Athaliah the mother of Ahaziah saw that her son was dead, she arose and destroyed all the seed royal." — 2 Kings 11:1 (ASV)

As the wife of Joram and mother of Ahaziah, Athaliah had guided both the internal and external policy of the Jewish kingdom. She secured the establishment of Baal worship in Judea (2 Kings 8:18, 27) and maintained a close alliance with the sister kingdom (2 Kings 8:29; 2 Kings 10:13).

The revolution carried out by Jehu deeply affected her. It removed the support of her relatives and isolated her religious system by cutting off communication with Phoenicia. Furthermore, the death of Ahaziah deprived her of her legal status in Judea as queen-mother (see note on 1 Kings 15:13), transferring that position to the chief wife of her deceased son.

Instead of yielding to the storm or merely standing on the defensive, Athaliah resolved to take the offensive, striking before any plans could be formed against her. In her son's absence, she likely held the chief authority in Jerusalem. She used this power to command the immediate destruction of David's entire family—already thinned by previous massacres (2 Kings 10:14; 2 Chronicles 21:4, 17)—and then seized the throne.