When lives are at stake, Judaism permits--and probably requires--fighting.
Excerpted and reprinted with permission from S'VARA 2:1 (1991).
The Jewish rationale for defensive war emerges in a talmudic discussion of when it is permissible to wage war on the Sabbath:
"Rav Judah stated in the name of Rav: 'If foreigners besieged Israelite towns, it is not permitted to sally forth against them or to desecrate the Sabbath in any other way on their account,' and a Tannaitic source teaches the same thing. This, however, applies only where they came for the sake of money matters, but if they came with the intention of taking lives, the people are permitted to sally forth against them with their weapons and to desecrate the Sabbath on their account. Where the attack, however, was made on a town that was close to a frontier [the loss of which would constitute a strategic danger to the other parts of the country], even though they did not come with any intention of taking lives but merely to plunder straw or hay, the people are permitted to sally forth against them with their weapons and to desecrate the Sabbath on their account." (Eruvin 45a)
Why is Self-Defense Permitted?
This passage establishes a justification for engaging in a category of war not mentioned in Deuteronomy 20 or in the talmudic analysis of obligatory and discretionary wars. Significantly, there is no explicit, biblical justification for engaging in defensive war. The rabbis do establish a duty of self‑defense for each individual on the basis of Exodus 22:1. As the Talmud puts it, "[I]f someone comes to kill you, get up early in the morning to kill him first." (Berakhot 58a; Yoma 85b; Sanhedrin 72a) Because each individual has both the right and the obligation of self‑defense, one might reasonably infer that the community does likewise.
Rabbi J. David Bleich, however, points out that there are significant problems in justifying defensive war in that way because of the restrictions placed upon the individual's right of self‑defense. Even if we expand our vision to encompass the obligation that each Jew has to intervene to stop a pursuer (rodef) from killing another person, we cannot, according to R. Bleich, find grounds from such instances of individual action to justify defensive war on this basis.
Bleich gives three reasons for his claim. First, because the obligation to stop the pursuer does not apply when that would endanger one's own life. Specific sanction beyond application of the law of pursuit is required in order to justify conscription, that is, coercion to endanger one's life in defending others.
Second, moreover, the law of pursuit may be invoked only in the face of imminent danger to life, but the Talmud sanctions defensive wars against border settlements even when the marauding forces seek only "straw or hay." Therefore additional sanction is necessary to justify a defensive war to ward off aggression when danger to life is not imminent.