Deuteronomy 20:8-11

Then the officers shall add, “Is anyone afraid or fainthearted? Let him go home so that his fellow soldiers will not become disheartened too.” When the officers have finished speaking to the army, they shall appoint commanders over it. When you march up to attack a city, make its people an offer of peace. If they accept and open their gates, all the people in it shall be subject to forced labor and shall work for you.