Deuteronomy 20:10-12

10When thou approachest unto a city to fight against it, thou shalt proclaim peace unto it.

11And it shall be, if it make thee answer of peace, and open unto thee, then all the people that are found therein shall be tributaries unto thee, and they shall serve thee.

12And if it will not make peace with thee, but will make war with thee, then thou shalt besiege it;