And they warred against the Midianites. It was a signal example of obedience, that 12,000 men did not refuse to engage in a war which was full of danger, when it was reasonable for them to object that it was not right for them to be exposed to butchery, as it were, whilst the people sat idly in the camp, who by their great numbers and with little trouble would have routed and overcome the enemy. It was therefore no common proof of piety, that they obeyed God's command, and sought for no pretext to cover their cowardice. God, too, shewed by the result that He did not rashly expose His servants to danger; for it is in His power to rescue those whom He takes under His protection, from a hundred deaths. From hence also we are taught that there is no surer means of safety than to follow whither He leads. What Moses afterwards adds, tends to render praise to their perseverance, with one exception, they were right in killing all the males, even to the kings, whom Moses relates to have been slain in the general slaughter; and especially that they inflicted punishment on Balaam, who by his cunning and his snares, had endeavored to destroy the people of God. They were right, too, in spoiling the whole land; nor did they act with less propriety and discretion in razing all the cities and towns, which might have been a temptation to the timid and inactive to take up their abode there; for, as we have seen before, all hindrances were to be taken away, so that the people might advance freely and without incumbrance into the land of Canaan; else, when there was an opportunity of repose, many would have willingly foregone the promised inheritance. Hence the cities were consumed by fire, lest they should afford any hold for those who were willing to stay. Thus far the selected soldiers faithfully performed their duty: in one respect they failed, in that, under the impulse either of avarice or lust, they preserved the women alive: on which point we shall see more presently.

And they warred against the Midianites, as the Lord commanded Moses,.... 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 (b) 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 would might escape for his life, as it is said, "and they warred against Midian, as the Lord commanded Moses"; by report, or from tradition, it is learnt that so he commanded him;''that is, in such a manner to besiege a city; but for this there is only tradition, for it is not mentioned among the rules after directed to in such a case, Deuteronomy 20:10,
and they slew all the males; which fell into their hands; for, no doubt, there were multitudes that made their escape, since in later times we read of the Midianites, as a very powerful people, and very distressing to Israel, Judges 6:1 these, as Aben Ezra observes, they slew, were such as were grown up, for as for their little ones, them they spared and carried captive, Numbers 31:9.
(b) Hilchot Melacim, c. 6. sect. 7.

The Israelites slew the Kings of Midian. They slew Balaam. God's overruling providence brought him thither, and their just vengeance found him. Had he himself rightly believed what he had said of the happy state of Israel, he would not have thus herded with the enemies of Israel. The Midianites' wicked wiles were Balaam's projects: it was just that he should perish with them, Hosea 4:5. They took the women and children captives. They burnt their cities and castles, and returned to the camp.

they slew all the males--This was in accordance with a divine order in all such cases (Deuteronomy 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 (Numbers 25:1-3), while a large portion of the Midianites were absent on their pastoral wanderings or had saved themselves by flight. (Compare Judges 6:1).

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 Numbers 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 Numbers 25:15. In Joshua 13:21 they are called "vassals of Sihon," because Sihon had subjugated them and made them tributary when he first conquered the land. The women and children of the Midianites were led away prisoners; and their cattle (behemah, beasts of draft and burden, as in Exodus 20:10), and their flocks, and their goods taken away as spoil. The towns in their dwellings, and all their villages (tiroth, tent-villages, as in Genesis 25:16), were burnt down. The expression "towns in their dwellings" leads to the conclusion that the towns were not the property of the Midianites themselves, who were a nomad people, but that they originally belonged in all probability to the Moabites, and had been taken possession of by the Amorites under Sihon. This is confirmed by Joshua 13:21, according to which these five Midianitish vassals of Sihon dwelt in the land, i.e., in the kingdom of Sihon. This also serves to explain why the conquest on their country is not mentioned in the account before us, although it is stated in Joshua (l.c.), that it was allotted to the Reubenites with the kingdom of Sihon.

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, Deuteronomy 20:13, only their fault was, that they did not consider the special reason which they had to involve the women in the destruction.