Judges 20:25
And Benjamin went forth against them out of Gibeah the second day, and destroyed down to the ground of the children of Israel again eighteen thousand men; all these drew the sword. And Benjamin went forth against them out of Gibeah the second day, and destroyed down to the ground of the children of Israel again eighteen thousand men; all these drew the sword.
On the second day of the civil war the Benjamites went forth out of Gibeah against Israel and destroyed to the ground eighteen thousand Israelite men, all of them men who drew the sword. This was Israel's second defeat by Benjamin at Gibeah in that campaign against the wicked Benjamites. Though twice repulsed, Israel was sent against Benjamin a third time, and only then finally overcame them.
The battle followed the outrage against the Levite's concubine and the crime at Gibeah. The tribe of Benjamin had identified itself with wicked Gibeah, and Israel's conflict with Benjamin for that cause brought severe losses. The verse belongs to the closing chapters of Judges, describing the troubled times of the judges and the early period of the judges. It was when the ark of the covenant was at Bethel, where the people came to inquire of the Lord, and it was before the call of Samuel the prophet. The conflict was one that nearly wiped out the tribe of Benjamin.
As part of that history the verse records Israel's repeated backsliding and the low, fallen state into which Israel had come. That backsliding brought disgrace and punishment and severe losses in battle. This history of Israel's low condition in the time of the judges stands in mighty contrast to the miracles and teaching of Jesus in Luke, yet together with them it speaks of the goodness and mercy of God.
Israel's being twice repulsed before final victory shows that God may allow His people to suffer apparent defeat for a time before giving them victory. The devastating civil war had once left Benjamin nearly extinct, and choosing Israel's king from this small tribe could remove grounds for jealousy among the other tribes.