Albert Barnes Commentary Judges 20:48

"And the men of Israel turned again upon the children of Benjamin, and smote them with the edge of the sword, both the entire city, and the cattle, and all that they found: moreover all the cities which they found they set on fire." — Judges 20:48 (ASV)

They treated Benjamin as devoted to utter destruction, as Jericho had been (Joshua 6:17, Joshua 6:21), and the whole tribe was virtually extirpated. We see in the punishment inflicted the same ferocity that marked both the crime and the Levite’s method of demanding vengeance.