Deuteronomy 20:10-15

Before you attack a town that is far from your land, offer peace to the people who live there. If they surrender and open their town gates, they will become your slaves. But if they reject your offer of peace and try to fight, surround their town and attack. Then, after the LORD helps you capture it, kill all the men. Take the women and children as slaves and keep the livestock and everything else of value.