There was no war between Syria and Israel for three years. ¹ 

“You know what Joab son of Zeruiah did to me – how he murdered two commanders of the Israelite armies, Abner son of Ner and Amasa son of Jether. ¹  During peacetime he struck them down like he would in battle; ²  when he shed their blood as if in battle, he stained his own belt and the sandals on his feet. ³ 

When Rehoboam arrived in Jerusalem, he summoned 180,000 skilled warriors from all of Judah and the tribe of Benjamin ¹  to attack Israel and restore the kingdom to Rehoboam son of Solomon.