Deuteronomy 20:10-15

10“When you advance to a city to fight against it, you shall [first] offer it terms of peace.

11If that city accepts your terms of peace and opens its gates to you, then all the people who are found in it shall become your forced labor and shall serve you.

12However, if it does not make peace with you, but makes war against you, then you shall lay siege to it.

13When the Lord your God gives it into your hand, you shall strike down all the men in it with the edge of the sword.

14Only the women and the children and the animals and everything that is in the city, all its spoil, you shall take as plunder for yourself; and you shall use the spoil of your enemies which the Lord your God has given you.

15That is what you shall do to all the cities that are very far away from you, which are not among the cities of these nations nearby [which you are to dispossess].