Absalom had put Amasa in charge of the army to replace Joab. Amasa was the son of a man named Ithra, the Ishmaelite who lived with Abigail, the daughter of Nahash and sister of Zeruiah, Joab's mother.
All the Israelites from Dan to Beersheba, including the land of Gilead, went and gathered at Mizpah before the Lord. The assembly was united in purpose.