Deuteronomy 20:10-12

“When you draw near to a city to fight against it, then proclaim peace to it. It shall be, if it makes you answer of peace, and opens to you, then it shall be, that all the people who are found therein shall become forced laborers to you, and shall serve you. If it will make no peace with you, but will make war against you, then you shall besiege it.”