21 When Rehoboam arrived in Jerusalem, he mustered all Judah and the tribe of Benjamin—a hundred and eighty thousand able young men—to go to war against Israel and to regain the kingdom for Rehoboam son of Solomon.

Read 1 Kings 12:21 Using Other Translations

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.
When Rehoboam came to Jerusalem, he assembled all the house of Judah and the tribe of Benjamin, 180,000 chosen warriors, to fight against the house of Israel, to restore the kingdom to Rehoboam the son of Solomon.
When Rehoboam arrived at Jerusalem, he mobilized the men of Judah and the tribe of Benjamin—180,000 select troops—to fight against the men of Israel and to restore the kingdom to himself.