This chapter contains regulations for war in general (vv1-15) and for war within the confines of the land God had given them (vv16-20).

‘The passage is describing “holy war” (sometimes called “Yahweh war”), a conflict initiated by the Lord, empowered by Him, and resulting in His appropriation of its spoils. Such warfare was undertaken to destroy peoples who were irretrievably beyond redemption and who were likely to contaminate Israel’s faith with their idolatrous practices (see 1:30; 7:2, 16; 19:1).’ (Apologetics Study Bible)

Laws Concerning War with Distant Enemies, 1-15

20:1 When you go to war against your enemies and see chariotry and troops who outnumber you, do not be afraid of them, for the LORD your God, who brought you up out of the land of Egypt, is with you.

In vv1-4, the main point is that the people do not need to be afraid, because the battle is the Lord’s.  This is underlined by the role of the priest before battle, v2ff.

20:2 As you move forward for battle, the priest will approach and say to the soldiers, 20:3 “Listen, Israel! Today you are moving forward to do battle with your enemies. Do not be fainthearted. Do not fear and tremble or be terrified because of them, 20:4 for the LORD your God goes with you to fight on your behalf against your enemies to give you victory.” 20:5 Moreover, the officers are to say to the troops, “Who among you has built a new house and not dedicated it? He may go home, lest he die in battle and someone else dedicate it. 20:6 Or who among you has planted a vineyard and not benefited from it? He may go home, lest he die in battle and someone else benefit from it. 20:7 Or who among you has become engaged to a woman but has not married her? He may go home, lest he die in battle and someone else marry her.” 20:8 In addition, the officers are to say to the troops, “Who among you is afraid and fainthearted? He may go home so that he will not make his fellow soldier’s heart as fearful as his own.” 20:9 Then, when the officers have finished speaking, they must appoint unit commanders to lead the troops.

It is clear from vv5-8 that Israel did not have a standing army at this time.  The soldiers were ordinary citizens.  Exemptions were given to various groups whose domestic responsibilities (or whose fear, v8!) excused them from military service.

20:10 When you approach a city to wage war against it, offer it terms of peace. 20:11 If it accepts your terms and submits to you, all the people found in it will become your slaves. 20:12 If it does not accept terms of peace but makes war with you, then you are to lay siege to it. 20:13 The LORD your God will deliver it over to you and you must kill every single male by the sword. 20:14 However, the women, little children, cattle, and anything else in the city—all its plunder—you may take for yourselves as spoil. You may take from your enemies the plunder that the LORD your God has given you. 20:15 This is how you are to deal with all those cities located far from you, those that do not belong to these nearby nations.

The terms of engagement, vv10-15, are reasonably humane for the period.

v14 In the ancient world, soldiers were not paid a wage.  Rather, they were allowed a portion of the plunder from their conquests.

Laws Concerning War with Canaanite Nations, 16-20

20:16 As for the cities of these peoples that the LORD your God is going to give you as an inheritance, you must not allow a single living thing to survive. 20:17 Instead you must utterly annihilate them—the Hittites, Amorites, Canaanites, Perizzites, Hivites, and Jebusites—just as the LORD your God has commanded you, 20:18 so that they cannot teach you all the abhorrent ways they worship their gods, causing you to sin against the LORD your God. 20:19 If you besiege a city for a long time while attempting to capture it, you must not chop down its trees, for you may eat fruit from them and should not cut them down. A tree in the field is not human that you should besiege it! 20:20 However, you may chop down any tree you know is not suitable for food, and you may use it to build siege works against the city that is making war with you until that city falls.

v17 The practice of total destruction (rather than taking prisoners or spoils) was used only sparingly in the ancient world.  In the case of the Israelites, total destruction was called for in the case of Jericho, Josh 6:17–24, Hazor, Josh 11:10–11, Zephath, Judges 1:17, and the Amalekites 1 Samuel 15:3.

See Num 31 for an account of this policy in action (but from a different point in the narrative).

Preston Sprinkle (Fight: A Christian Case For Non-Violence) writes:

‘Many critics such as Richard Dawkins will describe the conquest with a slanted view of these people. You would think that they were innocent peasants living peaceably with one another, when all of a sudden a sociopath named Joshua came in and slew all the women and children. But this is not the way the Bible presents the event. The Canaanites on the whole were a particularly wicked people by anyone’s standard. Incest, bestiality, orgiastic religious prostitution, and child sacrifice were a regular part of life. The Canaanite gods themselves were said to be engaged in shameless sexual feats, and the Canaanites joined in.’

And again:

‘God didn’t randomly pick on the Canaanites because they were the most wicked. Rather, He sought to drive them out of the land because the land would become God’s residence on earth. This means the Canaanites were having sex with prostitutes and sacrificing babies to foreign gods right there in God’s living room. Put simply: the Promised Land would become God’s new home on earth. Yes, God dwells in heaven. But biblically speaking, He also resides on earth—first in Eden, then in the tabernacle, and then in the temple. Since God is holy (set apart), His presence requires “sacred space,” and God chose the land of Canaan to be that sacred space—the piece of earth where His holy presence would dwell.’

v18 Enns observes that the stated rationale for this extermination is the protection of the Israelites (from the ‘detestable’ practices of the Canaanites) rather than the punishment of the Canaanites for those practices.  But it is difficult to see why we should distinguish so sharply between these two motives, especially as elsewhere (as Enns himself notes) the extreme sin of the Canaanites is held out to be the reason for their extermination (Gen 15:16; Deut 9:4), with the tipping point being Canaanite child sacrifice (Deut 12:31).  (On the latter point, Enns pleads that the Canaanites ‘had hardly cornered the market on this act’ – see 2 Kings 3:27 – but the truth is that such a practice is viewed with abhorrence throughout the OT).

v19 Environmental damage was to be kept to a mimimum.

‘The regulations for war in ch. 20 need to be used with great caution when principles are sought for the conduct of modern wars. The first requirement is to distinguish holy war from other kinds, even in Israel. Holy war is a concept which applies only, once and for all, to Israel’s occupation of its God-given land. Even Israel’s wars in general are special, because at that period in the history of God’s dealing with humanity his people was also a nation, a political unit. Now that that people is a church, which fights no wars as such, no nation has a mandate to suppose that God marches in its ranks in the wars that it fights—even where those wars may reasonably be thought just.’ (NBC)

Christopher Wright discusses how the principle of love for neighbour can be operative in the context of war.  He makes two points.  Firstly, love for neighbour does not mean a facile ‘niceness’ that is incompatible with punishment of idolatry or murder.  Similarly, the meting out of divine justice on the Canaanites is not incompatible with God’s larger purposes regarding the blessing of all nations.  Furthermore, this justice is not incompatible with the compassion and protection afforded to the foreigner.  Secondly, we have to reckon with the fallenness of human nature within which love for neighbour has to operate.  Sometimes it is necessary ‘to work for the humane within the humane, to mitigate the worst effects of human sin’ not only in the face of the realities slavery and divorce, for example, but also (as in this chapter) in the face of terminal wickedness.