The problem is that in 1 Kings 11, Jeroboam is told he will receive 10 tribes, with 2 remaining with Rehoboam. But the territory of the tribe of Simeon was entirely within the tribe of Judah, so how did Jeroboam get 10 ‘pieces’ if Judah, Benjamin and Simeon remained with Rehoboam?
Well, one of the most intriguing aspects of the 12 tribes is that there were actually 13, since Joseph got two tribes: Ephraim and Manassah. But it was always 12 tribes whenever described or listed. So the question always was, which tribe misses out and why? Sometimes it was Levi, the landless tribe. Sometimes Ephraim and Manassah were collapsed into Joseph (Ezekiel 48), and other times Dan (Eze 48; Rev 7) missed out.
But in 1 Kings 11, there are only eleven tribes (v31-32):
Then he said to Jeroboam, “Take ten pieces for yourself, for this is what the LORD, the God of Israel, says: ‘See, I am going to tear the kingdom out of Solomon’s hand and give you ten tribes. But for the sake of my servant David and the city of Jerusalem, which I have chosen out of all the tribes of Israel, he will have one tribe.
Hmm, 13 tribes and 2 missing this time? Well, we know that the Levites sided with Rehoboam (2 Chron 11:13-14), and Benjamin went with Judah (2 Kings 12 — in the army). So how to resolve this?
I suppose that Simeon could indeed side with the ten tribes, and simply migrate into a new homeland, much as Dan did in Judges 18. That’s a possible solution, though I’m not sure how convincing it is. As for one tribe with Rehoboam, I’m inclined to think that there’s an implicit “other” — Rehoboam will have one tribe other than Judah.
So this brings us back to 12 tribes, with the tentative notion that Simeon abandoned ship and land to join the ten tribes in the north.
This is supported by 2Chron 34:6-7:
In the towns of Manasseh, Ephraim and Simeon, as far as Naphtali, and in the ruins around them, Josiah tore down the altars and the Asherah poles and crushed the idols to powder and cut to pieces all the incense altars throughout Israel.
A similar passage can be found in 2 Chron 15:9.