Two Types of Jewish War
Judaism distinguishes between commanded wars and permitted wars.
Excerpted and reprinted with permission from S'VARA 2:1 (1991).
The major biblical statement on morality of war, Deuteronomy 20, differentiates between two types of war. As to "towns that lie very far from you, towns that do not belong to nations hereabout" (verse 15), wars of conquest are permissible. As stated, these are wars against enemies that lie very far from Israel's borders, and as such, are obviously not defensive wars but rather wars motivated by pure aggression.
As to "towns of the latter peoples [who inhabit the land Canaan]…which the Lord your God is giving you as a heritage" (verse 16), the justification for war is the Jewish people's exercising their divine right to the land of Canaan, "And you shall take possession of the land and settle in it for I have assigned the land to you to possess."
The Threat of Idolatry
This divine right of conquest is not, however, the justification for the eradication of the seven nations from the land of Canaan, but rather the belief that "they [will] lead you into doing all the abhorrent things that they have done for their gods and you stand guilty before the Lord your God." (verse 18)
The Bible perceives these nations as threatening not simply the political survival of the Jewish people, but also the continuity of the covenant. According to the conventional view, monotheistic ideology had yet to take a serious hold on the Jewish people and the idolatrous practices of the people surrounding them were far more attractive and enticing. The Bible recognizes this threat as determinative of the interaction between the Israelites and their neighbors.
The fear of foreign contamination locates Deuteronomy 20 in its historical context and therefore inhibits attempts (especially in the modern Israeli context) to transform the biblically sanctioned war against the seven nations into a model for war against all non‑Jewish enemies of the Jewish people who either inhabit the land of Israel or who threaten her existence. The creation of a totally "Israelized" State of Israel is biblically prescribed only in the context of an idolatrous enemy such as the seven nations of antiquity, whose threat was theological and not simply political.
Jewish Wars of Aggression
By contrast, war against nations "that lie very far from you" cannot be justified as a form of religious self‑defense. As typified by the wars during the reigns of kings David and Solomon, they are wars of pure expansion and aggression. Yet they too are God's wars:
"…and when the Lord your God delivers it into your hand (verse 13)…and enjoy the use of the spoil of your enemy, which the Lord your God gives you (verse 14)."