In these two verses we have again the same curious juxtaposition of “the tribe of Judah only” and “the house of Judah, with the tribe of Benjamin.” The army gathered would be, no doubt, drawn from Solomon’s established and disciplined forces, as well as from the levy of Judah and Benjamin generally — perhaps including (as in 2 Samuel 17:27) contingents from the tributary races — who would be attached with a strong personal allegiance to the house of Solomon, and prepared to stamp out the rebellion, before it could thoroughly organise itself for disciplined resistance.
Related Commentaries of 1 Kings 12:20
1 Kings 12:20-21
20 And it came to pass, when all Israel heard that Jeroboam was come again, that they sent and called him unto the congregation, and made him king over all Israel: there was none that followed the house of David, but the tribe of Judah only.
21 And when Rehoboam was come to Jerusalem, he assembled all the house of Judah, with the tribe of Benjamin, an hundred and fourscore thousand chosen men, which were warriors, to fight against the house of Israel, to bring the kingdom again to Rehoboam the son of Solomon.