John Gills Exposition of the Bible Commentary - Numbers 31:9
And the children of Israel took all the women of Midian captives ,.... The word "all" is not in the original text, nor should it be supplied; for if all had been taken, and carried captive, and put to death, as those were afterwards, how could there have been such an increase of the Midianites as there was in some time after this? see Judges 6:1 but the meaning is, that as many as fell into their hands they took and carried captive: and their little ones ; both male and female: ... read more
Matthew Henry's Complete Commentary - Numbers 31:7-12
Here is, 1. The descent which this little army of Israelites made, under the divine commission, conduct, and command, upon the country of Midian. They warred against the Midianites. It is very probable that they first published their manifesto, showing the reasons of the war, and requiring them to give up the ringleaders of the mischief to justice; for such afterwards was the law (Deut. 20:10), and such the practice, Jdg. 20:12; 13. But the Midianites justifying what they had done, and... read more