A large portion of the second half of the Old Testament depicts the wars in which the Israelites engaged in occupying the land that the Lord had promised them. However, the rules of conduct for military engagements were laid out as early as Deuteronomy, which reassures the people first and foremost that the Lord will guide them successfully through their battles, however poor the odds:

“When thou goest out to battle against thine enemies, and seest horses, and chariots, and a people more than thou, be not afraid of them: for the Lord thy God is with thee, which brought thee up out of the land of Egypt.” (Deuteronomy 20:1)

But God does not necessarily promote warfare; indeed, he commands that peaceful measures first be employed to subdue the cities proposed to be conquered:

“When thou comest 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 is found therein shall be tributaries unto thee, and they shall serve thee.
And if it will make no peace with thee, but will make war against thee, then thou shalt besiege it:” (Deuteronomy 20:10-12)

In modern times we perceive war as a consequence of conflicts between countries rather than as a means of gaining tributes or territories; indeed, the international community frowns severely upon wars of conquest. But the old-fashioned Biblical view was not so; peace is offered only as a less bloody alternative to war. There is no discussion and no compromise; the end result will be the same whichever means is chosen: total subjugation of the city involved.

The treatment of the subjugated peoples, too, strikes the modern ear as hopelessly barbarian:

“And when the Lord thy God hath delivered it into thine hands, 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 unto thyself; and thou shalt eat the spoil of thine enemies, which the Lord thy God hath given thee.” (Deuteronomy 20:13-14)

And woe unto the particular enemies of the Lord, of whom not even the women and children shall be spared:

“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:
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:
That they teach you not to do after all their abominations, which they have done unto their gods; so should ye sin against the Lord your God.” (Deuteronomy 20:16-18)

Again we see the idea of the land itself becoming defiled by the acts of its inhabitants. Sodom and Gomorrah was destroyed with fire and brimstone; the land of the Israelites will be purged through warfare. Yet it is not to be a holy war according to the modern conception, in which the followers of one religion shall supersede another owing to any perceived superiority of faith or belief. War is not a symbol of the triumph of good over evil, or even a means of restoring historic territorial rights. Success in war is granted not as a reward for the righteous conduct of the chosen people, but rather as a punishment for the even more wicked peoples that preceded them:
    
“Not for thy righteousness, or for the uprightness of thine heart, dost thou go to possess their land: but for the wickedness of these nations the Lord thy God doth drive them out from before thee.” (Deuteronomy 9:5)