2 Chronicles 15:9

9. The strangers with them out of Ephraim and Manasseh The Israelites of these leading tribes of the northern kingdom are here spoken of as strangers. Such estrangement had secession wrought, Many of the more pious Israelites out of the various tribes joined the kingdom of Judah in the days of Rehoboam, but multitudes more came now when they saw that the Lord his God was with Asa.

And out of Simeon Most of the tribe of Simeon probably fell to the southern kingdom from the first, but not all the tribe, for there were not a few whose jealousy of Judah and Jerusalem led them to cast in their fortunes with the majority of the nation. Keil remarks that “the Simeonites, though politically united with Judah, yet in religious matters were not so, but had set up in Beersheba a worship of their own similar to that in Beth-el and Dan. In such a case the more earnest and thoughtful people from Simeon, as well as from Ephraim and Manasseh, may have gone to Jerusalem to the sacrificial festival prepared by Asa. In favour of this last supposition we may adduce the fact that the prophet Amos (1 Chronicles 4:4; 1 Chronicles 5:5; 1 Chronicles 8:14) mentions Beer-sheba, along with Beth-el and Gilgal, as a place to which pilgrimages were made by the idolatrous Israelites.”