Deuteronomy 20:10-13

10“When you go near a city to fight against it, then proclaim an offer of peace to it.

11And it shall be that if they accept your offer of peace, and open to you, then all the people who are found in it shall be placed under tribute to you, and serve you.

12Now if the city will not make peace with you, but makes war against you, then you shall besiege it.

13And when the Lord your God delivers it into your hands, you shall strike every male in it with the edge of the sword.