민수기 31:7의 Halakhah

From the laws of the commandment are what they, may their memory be blessed, said (Mishneh Torah, Laws of Kings and Wars 6:1) that the law of the call for peace is with every place - meaning to say whether in a commanded war or in an optional war. And a commanded war is, for example, [against] the seven [Canaanite] nations and Amalek. And [with] all, if they make peace with us - meaning to say, they took upon themselves the tax and servitude, and likewise that they took upon themselves the seven commandments - we do not kill a soul from them, and they will be for tribute and serve us. But when they do not make peace, there is a distinction between a commanded war and an optional: That in a commanded war, we do not keep a soul alive; whereas in an optional war we keep their infants and women alive, as we wrote adjacently. And likewise, in an optional war, we leave one side of a besieged city open, that they can run away from there, and as it is found in Sifrei Bamidbar 157. And we learn this from that which is written (Numbers 31:7), "And they gathered upon Midian as the Lord commanded." But in a war against the seven nations, we encircle them from all sides. However, we nonetheless inform them first that if their will is to leave the city and go away, the option is in their hand.