The start of this chapter gives a flashback to an oath that Israel had sworn at the earlier meeting at Mizpah (Judges 20:1–10). There, Israel not only decided to join forces to punish Gibeah but also made an oath that none of them would ever give his daughter to a Benjamite in marriage.1
1 Now the men of Israel had sworn at Mizpah, “No one of us shall give his daughter in marriage to Benjamin.”