War in Judaism is a complex issue. Some wars were Divinely ordained, for reasons known to G‑d alone. Others were necessary for self-defense or other purposes. The ultimate goal, however, is for the world to be at peace, as Isaiah prophesied: “He [Moshiach] shall judge between the nations and reprove many peoples, and they shall beat their swords into plowshares and their spears into pruning hooks; nation shall not lift the sword against nation, neither shall they learn war anymore.”1

1. Some Biblical-Era Wars Were Divinely Ordained

During the conquest of Canaan, the Jewish nation was commanded to eliminate the tribes that inhabited the land, in order to prevent their evil ways from spreading. According to the Jerusalem Talmud, these nations were given the opportunity to repent and accept upon themselves the Seven Noahide Laws. Only if they refused to accept this moral code and instead remained steadfast in their sinful ways was the command to be carried out.2

G‑d also commanded us to battle Amalek, the nation that attacked the people of Israel on their way out of Egypt: “Remember what Amalek did to you on the way, when you went out of Egypt . . . you shall obliterate the remembrance of Amalek from beneath the heavens. You shall not forget!”3

This category of war is known as milchemet mitzvah, a Divinely ordained war.

Read more about Amalek

2. Peace Must Be Proposed First

A telling directive as to how warfare should be carried out is found in Deuteronomy: “When you approach a city to wage war against it, you shall propose peace to it.”4 There is discussion amongst the rabbis as to whether this condition applies to Divinely ordained warfare (milchemet mitzvah) or only to a discretionary war (milchemet reshut). A discretionary war is one that is embarked upon by a king of Israel to secure or expand the borders of Israel. In order to embark on such a war, the king must obtain authorization from the Sanhedrin, the Jewish High Court5. According to Maimonides, this command applies to Divinely ordained wars as well.6

Listen: War in Jewish Law

3. Weapons Are Not Ornaments

In discussing the laws of carrying on Shabbat, the Mishnah underscores an important ethical idea. On Shabbat it is forbidden to carry an object four cubits in a public domain. Clothing or jewelry, which a person wears, is not considered to be in violation of this law, since you are not carrying your clothing. The Mishnah states that it is forbidden to go out wearing a sword or another weapon. Rabbi Eliezer objects, saying: “For him it is an ornament” (i.e., it should be permitted just as jewelry is). The rabbis respond: “They [weapons] are only a discredit [to those who wear them], as the verse states:7 ‘And they shall beat their swords into plowshares and their spears into pruning hooks . . .’”8 Ultimately, in the days of Moshiach, weapons will be transformed into tools that help mankind. Weapons represent a state of the world that we don't want to be in, and wearing them is no badge of honor, no symbol of beauty.

4. The Camp Must Be Holy

During war, special emphasis is placed on maintaining the purity and sanctity of the camp. As the verse tells us: “For the L‑rd, your G‑d, goes along in the midst of your camp, to rescue you and to deliver your enemies before you. [Therefore,] your camp shall be holy, so that He should not see anything unseemly among you, and turn away from you.”9 The Torah provides practical examples as to how the camp should be kept clean and pure. For instance, the troops were to carry a tool with which to dig and cover their waste after relieving themselves.10 Additionally, the Torah strongly emphasizes the importance of a superior level of morality. The verse states: “When you go forth against your enemies and are in camp, then you shall keep yourself from every evil thing.”11 The Midrash interprets this to refer to various forms of depraved behavior, which the army was to avoid.12

5. Newlyweds and Others Would Stay Home

Before battle, a kohen and an officer would address the troops, giving inspiration and also the opportunity for some soldiers to withdraw from battle. The kohen would proclaim: “Hear, O Israel, today you are approaching the battle against your enemies. Let your hearts not be faint; you shall not be afraid, and you shall not be alarmed, and you shall not be terrified because of them.” The officer would continue: “What man is there who has built a new house and has not inaugurated it? And what man is there who has planted a vineyard, and has not [yet] redeemed it? And what man is there who has betrothed a woman and has not [yet] married her? Let him go and return to his house, lest he die in battle . . .”

The officer would also give an opportunity for those who may have been fainthearted to return home, lest their lack of morale affect their fellow soldiers.13 Rashi here, quoting the Talmud,14 points out that this faintheartedness could also refer to one whose sins made him afraid, for he felt that he was unworthy and would therefore not survive the battle.

6. King David’s Warring Prevented Him From Building the Temple

G‑d tells King David: “You have shed much blood, and you have waged great wars; you shall not build a house in My name, because you have shed much blood to the ground before Me.”15 Although King David was not necessarily wrong for waging all those battles, the Temple was to be a place of peace. As such, it was to be built by King David’s son Solomon, a man more suited to the peaceful nature of the Temple.

Read: Was King David Wrong for Waging So Many Battles?

7. During a Siege, a Side of the City Must Be Left Open

An interesting and enigmatic condition to siege warfare is found in Maimonides’ Mishneh Torah: “When a siege is placed around a city to conquer it, it should not be surrounded on all four sides, only on three. A place should be left for the inhabitants to flee and for all those who desire to escape with their lives, as it is written: ‘They besieged Midian as G‑d commanded Moses.’ According to tradition, He commanded them to array the siege as described.”16 Again, there is discussion as to whether this law applies to both categories of war, or if it would apply only in a case of a discretionary war.

8. One Life Is No More Valuable Than Another

A famous case is cited in the Jerusalem Talmud regarding a group of Jews who are ambushed by non-Jews. The gentiles give them an ultimatum: either hand over a single Jew to be killed, or the entire group will be killed.17 The law is that no single Jew may be handed over; the entire group must give up their lives.18 The Lubavitcher Rebbe explains the rationale behind this law: Since a Jew’s soul is an actual part of the infinite G‑d, two souls are no more an expression of G‑d than one soul. We humans cannot be the arbiters of justice, to decide who shall live and who shall perish.19 Even at a time of war it must be remembered that human life is precious, and all must be done to avoid unnecessary death.

9. We Are at War With Our Evil Inclination

We as Jews are fighting a constant battle against our evil inclination (yetzer hara). In fact, our very purpose in this physical and mundane world is to ultimately triumph in this principal battle. This is achieved through the steadfast observance of Torah and mitzvahs. Our ultimate reward for persevering in this battle is the final redemption, a time where there will be no battles, a time when the world will finally be at peace.

10. We Are at War With War Itself

Rabbi Sholom DovBer, the fifth Rebbe of Chabad-Lubavitch, devoted an entire treatise to the war we must each wage against interpersonal divisiveness. Rather than choose a passage that commands love of one’s fellow or the like, he begins with a passage commanding a genocidal war against the Midianite nation:

The L‑rd spoke to Moses saying, “Wage the vengeance of the Israelites against the Midianites . . .” So Moses spoke to the people, saying, “. . . Carry out the vengeance of G‑d against Midian.”20

Midian, Rabbi Sholom DovBer tells us, is a conjugate of the Hebrew word madon, meaning “feud or quarrel.” In a direct inversion of their literal meaning, these passages are to be read as commanding a genocidal war against quarrelsomeness, a campaign to erase the egotistical divisiveness that is rooted in our own souls. Moses terms this war “the vengeance of G‑d,” which implies that quarrelsomeness is not merely a social ill, but a sin against G‑d. In other words, the real war we need to wage is the war against war itself.

Read more about Rabbi Sholom DovBer’s manifesto against self-righteousness and quarrelsomeness