Charles Ellicott Commentary Deuteronomy 20:10-20

"When thou drawest nigh unto a city to fight against it, then proclaim peace unto it. And it shall be, if it make thee answer of peace, and open unto thee, then it shall be, that all the people that are found therein shall become tributary unto thee, and shall serve thee. And if it will make no peace with thee, but will make war against thee, then thou shalt besiege it: and when Jehovah thy God delivereth it into thy hand, thou shalt smite every male thereof with the edge of the sword: but the women, and the little ones, and the cattle, and all that is in the city, even all the spoil thereof, shalt thou take for a prey unto thyself; and thou shalt eat the spoil of thine enemies, which Jehovah thy God hath given thee. Thus shalt thou do unto all the cities which are very far off from thee, which are not of the cities of these nations. But of the cities of these peoples, that Jehovah thy God giveth thee for an inheritance, thou shalt save alive nothing that breatheth; but thou shalt utterly destroy them: the Hittite, and the Amorite, the Canaanite, and the Perizzite, the Hivite, and the Jebusite; as Jehovah thy God hath commanded thee; that they teach you not to do after all their abominations, which they have done unto their gods; so would ye sin against Jehovah your God. When thou shalt besiege a city a long time, in making war against it to take it, thou shalt not destroy the trees thereof by wielding an axe against them; for thou mayest eat of them, and thou shalt not cut them down; for is the tree of the field man, that it should be besieged of thee? Only the trees of 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 fall." — Deuteronomy 20:10-20 (ASV)

Deuteronomy 20:10–20. SIEGES.

When thou comest nigh ... proclaim peace. —Not as the children of Dan did, who massacred the inhabitants of Laish without warning (Judges 18:27–28). Even in the wars of Joshua, the cities that stood still in their strength were generally spared (Joshua 11:13).

Thus — i.e., sparing the women and the little ones.

But of the cities of these people ... thou shalt save alive nothing that breatheth ... that they teach you not to do after all their abominations. —Upon the inhabitants of these cities the Israelites executed the sentence of Jehovah. Their abominations are sufficiently indicated in Leviticus 18:24-28; Leviticus 20:23.

These verses (16-18) are parenthetical; Deuteronomy 20:19 returns to the previous subject.

And thou shalt not cut them down (for the tree of the field is man’s life). —Literally, the passage seems rather to mean this: Is the tree of the field a man, that it should escape you and enter into the siege? It will not run away and fight in the trenches as a man might do. What need is there to cut it down?

This seems to be the view of the Targums, the Septuagint, and the Jewish commentators, besides modern authorities cited in the Variorum Bible.

The destruction of the trees around Jerusalem was a notable feature of the Roman war.