Out of Simeon; which tribe, though they had their inheritance out of the portion of Judah, did for the generality of them revolt to Jeroboam with the other tribes, as appears from many passages of Scripture; which they might conveniently do, because their portion bordered, as on one side upon that of Judah, so on the other side upon that of Dan; and therefore might indifferently join with the one or other, as they saw fit. They fell to him, to wit, from the king of Israel.
Related Commentaries of 2 Chronicles 15:9
2 Chronicles 15:9
9 And he gathered all Judah and Benjamin, and the strangers with them out of Ephraim and Manasseh, and out of Simeon: for they fell to him out of Israel in abundance, when they saw that the LORD his God was with him.