Numbers 31:7

“And they warred against the Midianites, as the Lord commanded Moses, etc.] Whether the Midianites came out against them with an army, and there was a pitched battle between them, is not certain; however the Israelites committed acts of hostility upon them, by entering their cities, plundering their houses, and slaying the inhabitants of them; the Targum of Jonathan is, “they warred against Midian, and surrounded it in the three corners of it, as the Lord commanded Moses;” for, as Maimonides f454 observes from tradition, “when they besiege a city to take it, they do not surround it in the four corners of it, but in the three corners of it, and leave a place to flee out, that everyone that…”

“they slew all the males--This was in accordance with a divine order in all such cases (Deu 20:13). But the destruction appears to have been only partial--limited to those who were in the neighborhood of the Hebrew camp and who had been accomplices in the villainous plot of Baal-peor (Num 25:1-3), while a large portion of the Midianites were absent on their pastoral wanderings or had saved themselves by flight. (Compare Jdg 6:1).”

“All the males - Namely all who lived in those parts, for colonies of them, were sent forth to remoter places, which therefore had no hand either in their former sin, or in this present ruling. And herein they did according to God's own order concerning such people, Deu 20:13, only their fault was, that they did not consider the special reason which they had to involve the women in the destruction. Numbers 31:13”

“31:7 The Israelites killed all of the Midianite men in the particular groups they attacked from their camp in the plains of Moab (31:12), not all of the people who were part of the larger Midianite confederation (cp. Judg 6–8). The number of animals and virgins mentioned in Num 31:32-35 indicates that the 12,000 Hebrews fought a sizable enemy force.”

“all: Deu 20:13, Deu 20:14; Jdg 21:11; Sa1 27:9; Kg1 11:15, Kg1 11:16 the males: Jdg 6:1, Jdg 6:2, Jdg 6:33 Numbers 31:8”

“Of the campaign itself, the results are all that is recorded. No doubt it terminated with a great battle, in which the Midianites were taken unawares and completely routed. As it was a war of vengeance of Jehovah, the victors slew all the males, i.e., all the adult males, as the sequel shows, without quarter; and "upon those that were slain," i.e., in addition to them, the five Midianitsh kings and Balaam, who first advised the Midianites, according to Num 31:16, to tempt the Israelites to idolatry. The five kings were chiefs of the larger or more powerful of the Midianitish tribes, as Zur is expressly said to have been in Num 25:15. In Jos 13:21 they are called "vassals of Sihon," because…”