What does 1 Kings 12:21 mean?

When Rehoboam got back to Jerusalem, he gathered all the people from Judah and the tribe of Benjamin—about 180,000 trained soldiers—to fight against Israel and win the kingdom back for himself. 1 Kings 12:21 - Modern Text Bible

(Rehoboam, David’s grandson, tries to use force to reunite the kingdom, showing how tense and serious the split was.)