““Have you let every female live? ” he asked them. “Yet they are the ones who, at Balaam’s advice, incited the Israelites to unfaithfulness against the Lord in the Peor incident, so that the plague came against the Lord’s community.”
Numbers 31:15-16 HCSB
https://www.bible.com/72/num.31.15-16.hcsb
The war against the Midianites was out of vengeance. Part of this vengeance is because the women had relations with the men and caused them to stray. This was as much vengeance from the Lord as anything. The Lord used the Israelites to exact His vengeance on them.
The Lampstand 