Deuteronomy 20:10-15

10When you approach a city to fight against it, you are to make an offer of peace. 11If they accept your offer of peace and open their gates, all the people there will become forced laborers to serve you.

12But if they refuse to make peace with you and wage war against you, lay siege to that city. 13When the LORD your God has delivered it into your hand, you must put every male to the sword. 14But the women, children, livestock, and whatever else is in the city—all its spoil—you may take as plunder, and you shall use the spoil of your enemies that the LORD your God gives you. 15This is how you are to treat all the cities that are far away from you and do not belong to the nations nearby.