1 Kings 12:21
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.
After his irreparable mistake at Shechem, Rehoboam prepared to fight the house of Israel to bring the kingdom back to himself. That mistake was an unwise and unfeeling exercise of power that revealed pride of position and authority, failed to understand God's purpose for Israel, refused the people's request for decided reforms in government, and announced the intention to perpetuate and add to the evils introduced in Solomon's reign. Many thousands among the tribes, thoroughly aroused over Solomon's oppressive measures, rebelled against the house of David, and the twelve tribes were divided, with Judah and Benjamin forming the lower kingdom of Judah under Rehoboam and the ten northern tribes forming the kingdom of Israel under Jeroboam, in harmony with the prophet's prediction concerning the rending of the kingdom.
When Rehoboam came to Jerusalem, he assembled 180,000 chosen warriors from Judah and Benjamin to fight against the northern tribes, the house of Israel, to restore the kingdom to his own rule.
God did not allow Rehoboam to carry out the attack he proposed, but stopped it by instructing Rehoboam and the people through Shemaiah not to fight their Israelite brothers, because the division of the kingdom was from God. Rehoboam and the people obeyed God's instruction and returned home instead of fighting.