Deuteronomy 20:16-20 - Laws Concerning War With Canaanite Nations

¹⁶ But of the cities of these people which the LORD thy God doth give thee for an inheritance, thou shalt save alive nothing that breatheth: ¹⁷ But thou shalt utterly destroy them, namely, the Hittites, and the Amorites, the Canaanites, and the Perizzites, the Hivites, and the Jebusites, as the LORD thy God hath commanded thee: ¹⁸ That they may not teach you to do after all their abominations which they have done to their gods; so would ye sin against the LORD your God.

¹⁹ When thou shalt besiege a city a long time in making war against it to take it, thou shalt not destroy the trees of it by forcing an ax against them; for thou mayest eat of them: and thou shalt not cut them down (for the tree of the field is man's life) to employ them in the siege: ²⁰ Only the trees which thou knowest that they are not trees for food, thou shalt destroy and cut them down; and thou shalt build bulwarks against the city that maketh war with thee, until it shall be subdued.