God As Commander
Moses now discusses the principles governing warfare. These principles show that, despite the use of physical armaments, Israel was still to look to God for victory (Deuteronomy 20:1-9 Deuteronomy 20:1-9  When you go out to battle against your enemies, and see horses, and chariots, and a people more than you, be not afraid of them: for the LORD your God is with you, which brought you up out of the land of Egypt.
 And it shall be, when you are come near to the battle, that the priest shall approach and speak to the people,
 And shall say to them, Hear, O Israel, you approach this day to battle against your enemies: let not your hearts faint, fear not, and do not tremble, neither be you terrified because of them;
 For the LORD your God is he that goes with you, to fight for you against your enemies, to save you.
 And the officers shall speak to the people, saying, What man is there that has built a new house, and has not dedicated it? let him go and return to his house, lest he die in the battle, and another man dedicate it.
 And what man is he that has planted a vineyard, and has not yet eaten of it? let him also go and return to his house, lest he die in the battle, and another man eat of it.
 And what man is there that has betrothed a wife, and has not taken her? let him go and return to his house, lest he die in the battle, and another man take her.
 And the officers shall speak further to the people, and they shall say, What man is there that is fearful and fainthearted? let him go and return to his house, lest his brethren's heart faint as well as his heart.
 And it shall be, when the officers have made an end of speaking to the people that they shall make captains of the armies to lead the people.
American King James Version×). One of the threats that Israel would face in war mentioned in verse 1 is "horses and chariots." Armies equipped in this manner were particularly intimidating to foot soldiers. The commandment was given in Deuteronomy 17:16 Deuteronomy 17:16But he shall not multiply horses to himself, nor cause the people to return to Egypt, to the end that he should multiply horses: for as much as the LORD has said to you, You shall from now on return no more that way.
American King James Version×that Israel's kings not "multiply horses." And there is no evidence that Israel utilized horses for war before Solomon's time (1 Kings 4:26 1 Kings 4:26And Solomon had forty thousand stalls of horses for his chariots, and twelve thousand horsemen.
American King James Version×; 1 Kings 10:26 1 Kings 10:26And Solomon gathered together chariots and horsemen: and he had a thousand and four hundred chariots, and twelve thousand horsemen, whom he bestowed in the cities for chariots, and with the king at Jerusalem.
American King James Version×). If this is the case, it is particularly fitting that Moses assured Israel they need not fear even when armies came against them with chariots.
With Almighty God as commander, there was no room for fear in the ranks—and those who were fearful were to be excused (verse 8). Others excused from warfare—at least on a temporary basis—included a person who had just built a new house, one who had planted a new vineyard, and one who was betrothed to a woman to marry her (verses 5-7). Deuteronomy 24:5 Deuteronomy 24:5When a man has taken a new wife, he shall not go out to war, neither shall he be charged with any business: but he shall be free at home one year, and shall cheer up his wife which he has taken.
American King James Version×adds the further exception of a man who had just gotten married—he was permitted to stay with his wife for one year without having to go out to war. One of the reasons for these excuses from participation in battle seems to be that persons in such conditions would likely be thinking about what they were leaving behind rather than concentrating on the battle. No doubt, God's mercy and compassion are also shown in these regulations. Furthermore, in these "excused absences," God was showing that it is not necessary to rely on numbers. With God fighting for His people (verse 4), very few people could easily overcome a force of many times their number (see Leviticus 26:8 Leviticus 26:8And five of you shall chase an hundred, and an hundred of you shall put ten thousand to flight: and your enemies shall fall before you by the sword.
American King James Version×), as often happened during the Israelites' history when they were obedient to God.
Before the Israelites attacked a city "very far" from them (Deuteronomy 20:15 Deuteronomy 20:15Thus shall you do to all the cities which are very far off from you, which are not of the cities of these nations.
American King James Version×), they had to offer peace to it (verses 10-11). It is interesting that the offer was of peace—not enslavement. Such cities were to pay tribute, essentially a tax, and "serve" Israel—not in slavery but to remain in peace and harmony with Israel, thus promoting the safety, security and well-being of God's people. Moreover, in agreeing to keep Israel's laws and way of life, such cities would in fact enter into a much better way of life than they had ever known. If a city refused the offer and chose war instead, Israel was to "strike every male in it with the edge of the sword" (verses 12-13), while leaving the women and children alive (verse 14). In regard to the cities that were located within the Promised Land, however, Israel was to "let nothing that breathes remain alive" (verse 16), so that the evil inhabitants could not influence Israel with "their abominations...and you sin against the Lord your God" (verse 18).
Finally, God told Israel not to cut down fruit trees in a siege against a city. They were only allowed to destroy those trees that were not "trees for food" (verses 19-20). This would especially make sense in a longer siege where food supplies could become an issue.