He had told the Israelites they should not intermarry with other nations.
Numbers 31:1 - 51
MSG - 1 God spoke to Moses: "Avenge the People of Israel on the Midianites. Afterward you will go to be with your dead ancestors. 3 Moses addressed the people: "Recruit men for a campaign against Midian, to exact God's vengeance on Midian, a thousand from each tribe of Israel to go to war.
For follow-up discussion and general commentary on the topic. Comments are sorted chronologically.
Wasn't Moses wife also a Midianite? As would have been his father-in-law and of course his mother -in-law and their families? If so, could this have influenced this decision?
Yes, Moses wife, Zippora, was a Midianite. Moses was a foreigner in their land when he fled Egypt. Abraham, the father of our faith was a non-Jew also.
I cannot find anything to indicate that these young girls became slaves. I would like to think that they converted from isolatry to the true God. Moses family did I believe.
In Jesus lineage, Ruth is there, so is Abraham. Maybe the girls converted and survived, and went on to live in Canaan.
Ruth, a Moabite woman, is another example. She called Naomi's God her God, Naomi's people her people.
No one can fully fathom God's plan.
Thank God for salvation is extended to us Gentiles who are not the natural branch.