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The Torah commands the army to act as morally as possible, even during wartime. Therefore, before going to war with even our worst enemy – Amalek – there is a mitzva to first offer peace. As it says, “When you approach a town to attack it, you shall offer it terms of peace” (Deuteronomy 20:10). This means offering the enemy dignified terms of surrender, in which they have an autonomous state under Jewish rule, paying taxes and observing the seven Noahide laws. We only go to war if they reject peace.
Our objective in war is to achieve a resounding victory which will quash any further enemy desires to engage in battle. Therefore in biblical times, when the norms of war were (at the least) to kill all the enemy’s men, the Jews were commanded to do this too, as it says, “When the Lord your God delivers it into your hand, you shall put all its males to the sword” (Deuteronomy 20:13). For had they not done so, there would definitely be additional fighting, and perhaps a Jewish defeat. In addition, had the Jews not followed the standard practice, the surrounding nations would have concluded that if they wanted to go to war against someone, the Jews were the best target. Winning against the Jews would be the worthwhile, but losing would have no major consequences.
Thus, Jewish war ethics demand two things. First, offer peace. Second, after victory, do not harm the enemy except as necessary and in accordance with the accepted norms. In biblical times, it was known that Jewish kings were kind. Some accommodated their enemies too much and ultimately succumbed to them (I Kings, ch. 20). Others, such as King David, followed the Torah’s guidance to strike a balance between might and mercy. Such kings led the Jews to many glorious victories and a long period of peace.
Today as well, the army should strive for resounding victory and the total submission of our enemies, while being careful not to go beyond what is necessary and accepted. Thank God, due to the influence of the Bible, great rabbis, and righteous gentiles, the world has advanced morally. It is now generally agreed upon that soldiers are not to be killed outside of battle, and civilians are not to be harmed unless they are protecting an enemy. At the same time, victory must be overwhelming, so it will serve as a long-term deterrent to our enemies, and so there will be a degree of measure-for-measure punishment. We simply do to them what they tried to do to us. In an extreme case, when there is a group of truly evil people who dedicate their lives to terror and destruction, we should fight them to the death, as the Torah instructs regarding Amalek (39:3 below).
