Maimonides included several laws of warfare in his listing of the 613 commandments in the Torah, and he placed them “last but not least.” To see them, scroll down to the bottom of http://www.jewfaq.org/613.htm.
It’s a complicated topic, one that I have spoken about frequently. We need to understand it, but understanding, alas, will not help us to overcome the helplessness we all feel in a world where the ethics of warfare have become so murky.
The great poet Yehuda Amichai probably expresses that frustration better than anyone. See his poem, "I Want to Die in My Own Bed," as one example, as well as "Temporary Poem of My Time". Check out the home page of this site. It’s very moving.
Amichai ironically died just days before the second intifada erupted. Despite his death, his quintessentially human voice became the “voice of Jacob” as the fires raged, however, even in translation.
Perhaps his most oft-cited poem with regard to warfare is “The Diameter of the Bomb.”
The diameter of the bomb was thirty centimeters