When Rehoboam got back to Jerusalem he called up the men of the tribes of Judah and Benjamin, 180,000 of their best soldiers, to go to war against Israel and recover the kingdom.
This is GOD's word: Don't march out; don't fight against your brothers the Israelites. Go back home, every last one of you; I'm in charge here." And they did it; they did what GOD said and went home.
The Levites left their pastures and properties and moved to Judah and Jerusalem because Jeroboam and his sons had dismissed them from the priesthood of GOD
Everyone from all the tribes of Israel who determined to seek the GOD of Israel migrated with the priests and Levites to Jerusalem to worship there, sacrificing to the GOD of their ancestors.
That gave a tremendous boost to the kingdom of Judah. They stuck with Rehoboam son of Solomon for three years, loyal to the ways of David and Solomon for this period.
Maacah was Rehoboam's favorite wife; he loved her more than all his other wives and concubines put together (and he had a lot--eighteen wives and sixty concubines who produced twenty-eight sons and sixty daughters!).
He was shrewd in deploying his sons in all the fortress cities that made up his defense system in Judah and Benjamin; he kept them happy with much food and many wives.