I Kings 11:35-36 - 10 tribes would be given to Jeroboam and one tribe (Judah) to Rehoboam. But doesn't that include Benjamin as well (I Kings 12:21)? Who are the 10 tribes of the Northern Kingdom and the 2 tribes of the Southern Kingdom?
"Now it happened at that time, when Jeroboam went out of Jerusalem, that the prophet Ahijah the Shilonite met him on the way; and he had clothed himself with a new garment, and the two were alone in the field. Then Ahijah took hold of the new garment that was on him, and tore it into twelve pieces. And he said to Jeroboam, "Take for yourself ten pieces, for thus says the LORD, the God of Israel: 'Behold, I will tear the kingdom out of the hand of Solomon and will give ten tribes to you (but he shall have one tribe for the sake of My servant David, and for the sake of Jerusalem, the city which I have chosen out of all the tribes of Israel), because they have forsaken Me, and worshiped Ashtoreth the goddess of the Sidonians, Chemosh the god of the Moabites, and Milcom the god of the people of Ammon, and have not walked in My ways to do what is right in My eyes and keep My statutes and My judgments, as did his father David. However I will not take the whole kingdom out of his hand, because I have made him ruler all the days of his life for the sake of My servant David, whom I chose because he kept My commandments and My statutes. But I will take the kingdom out of his son's hand and give it to you-ten tribes. And to his son I will give one tribe, that My servant David may always have a lamp before Me in Jerusalem, the city which I have chosen for Myself, to put My name there" (I Kings 11:35-36).
At first glance, you might wonder why Ahijah can't do basic math. He rips his garment into twelve pieces, tells Jeroboam to take 10 pieces and 1 piece will remain with Solomon's son Rehoboam. But 10 plus 1 doesn't equal 12! What happened to the last piece?
The answer is simple. Rehoboam was of the tribe of Judah. He retained that tribe and was given one more, which turns out to be the tribe of Benjamin (I Kings 12:21; II Chronicles 11:12). Even then, when the split occurred, some people chose sides and moved. Even within the territory of Judah, there were members of all the tribes (I Kings 12:17).