just war

(6) Our God spoke to us at Horeb, saying: You have stayed long enough at this mountain. (7) Start out and make your way to the hill country of the Amorites and to all their neighbors in the Arabah, the hill country, the Shephelah, the Negeb, the seacoast, the land of the Canaanites, and the Lebanon, as far as the Great River, the river Euphrates.

(8) See, I place the land at your disposal. Go, take possession of the land that God swore to your fathers Abraham, Isaac, and Jacob, to assign to them and to their heirs after them.

(2) באו ורשו GO IN AND POSSESS [THE LAND] — There is no one who will contest the matter, and you will not need to wage war. Indeed, had they not sent the spies, but had trusted in God's promise, they would not have needed weapons of war (cf. Sifrei Devarim 7).

(22) Then all of you came to me and said, “Let us send agents ahead to reconnoiter the land for us and bring back word on the route we shall follow and the cities we shall come to.” (23) I approved of the plan, and so I selected from among you twelve participants, one representative from each tribe. (24) They made for the hill country, came to the wadi Eshcol, and spied it out. (25) They took some of the fruit of the land with them and brought it down to us. And they gave us this report: “It is a good land that our God ה׳ is giving to us.” (26) Yet you refused to go up, and flouted the command of your God ה׳. (27) You sulked in your tents and said, “It is out of hatred for us that ה׳ brought us out of the land of Egypt, to hand us over to the Amorites to wipe us out. (28) What kind of place are we going to? Our brothers have taken the heart out of us, saying, ‘We saw there a people stronger and taller than we, large cities with walls sky-high, and even Anakites.’” (29) I said to you, “Have no dread or fear of them. (30) None other than your God ה׳, who goes before you, will fight for you, just as [God] did for you in Egypt before your very eyes, (31) and in the wilderness, where you saw how your God ה׳ carried you, as a householder carries his son all the way that you traveled until you came to this place. (32) Yet for all that, you have no faith in your God ה׳, (33) who goes before you on your journeys—to scout the place where you are to encamp—in fire by night and in cloud by day, in order to guide you on the route you are to follow.” (34) ה׳ heard your loud complaint and, becoming angry, vowed: (35) Not one of those involved, this evil generation, shall see the good land that I swore to give to your fathers— (36) none except Caleb son of Jephunneh; he shall see it, and to him and his descendants will I give the land on which he set foot, because he remained loyal to ה׳.— (37) Because of you ה׳ was incensed with me too, saying: You shall not enter it either. (38) Joshua son of Nun, who attends you, he shall enter it. Imbue him with strength, for he shall allot it to Israel.— (39) Moreover, your little ones who you said would be carried off, your children who do not yet know good from bad, they shall enter it; to them will I give it and they shall possess it. (40) As for you, turn about and march into the wilderness by the way of the Sea of Reeds.

(41) You replied to me, saying, “We stand guilty before ה׳. We will go up now and fight, just as our God ה׳ commanded us.” And [the men among] you each girded yourselves with war gear and recklessly started for the hill country. (42) But ה׳ said to me, “Warn them: Do not go up and do not fight, since I am not in your midst; else you will be routed by your enemies.” (43) I spoke to you, but you would not listen; you flouted יהוה’s command and willfully marched into the hill country. (44) Then the Amorites who lived in those hills came out against you like so many bees and chased you, and they crushed you at Hormah in Seir. (45) Again you wept before ה׳; but ה׳ would not heed your cry or give ear to you.

(1) we marched back into the wilderness by the way of the Sea of Reeds, as ה׳ had spoken to me, and skirted the hill country of Seir a long time. (2) Then ה׳ said to me: (3) You have been skirting this hill country long enough; now turn north. (4) And charge the people as follows: You will be passing through the territory of your kin, the descendants of Esau, who live in Seir. Though they will be afraid of you, be very careful (5) not to provoke them. For I will not give you of their land so much as a foot can tread on; I have given the hill country of Seir as a possession to Esau. (6) What food you eat you shall obtain from them for money; even the water you drink you shall procure from them for money. (7) Indeed, your God ה׳ has blessed you in all your undertakings. [God] has watched over your wanderings through this great wilderness; your God ה׳ has been with you these past forty years: you have lacked nothing. (8) We then moved on, away from our kin, the descendants of Esau, who live in Seir, away from the road of the Arabah, away from Elath and Ezion-geber; and we marched on in the direction of the wilderness of Moab. (9) And ה׳ said to me: Do not harass the Moabites or provoke them to war. For I will not give you any of their land as a possession; I have assigned Ar as a possession to the descendants of Lot.— (10) It was formerly inhabited by the Emim, a people great and numerous, and as tall as the Anakites. (11) Like the Anakites, they are counted as Rephaim; but the Moabites call them Emim. (12) Similarly, Seir was formerly inhabited by the Horites; but the descendants of Esau dispossessed them, wiping them out and settling in their place, just as Israel did in the land they were to possess, which ה׳ had given to them.—

(13) Up now! Cross the wadi Zered! So we crossed the wadi Zered. (14) The time that we spent in travel from Kadesh-barnea until we crossed the wadi Zered was thirty-eight years, until that whole generation of warriors had perished from the camp, as ה׳ had sworn concerning them. (15) Indeed, the hand of ה׳ struck them, to root them out from the camp until they were finished off. (16) When all the warriors among the people had died off,

Warriors. Citizens of age for war, from 20 years and older.

V. 14. אנשי המלחמה, those who were of military age at the time the scouts were sent and who should therefore have been active in the planned occupation of the land at the time, but who had shied away from this task out of God-forgotten faintheartedness.

(36) As for the agents whom Moses sent to scout the land, those who came back and caused the whole community to mutter against him by spreading calumnies about the land— (37) those who spread such calumnies about the land died of plague, by the will of ה׳. (38) Of those involved in going to scout the land, only Joshua son of Nun and Caleb son of Jephunneh survived. (39) When Moses repeated these words to all the Israelites, the people were overcome by grief.

(40) Early next morning [their fighting force] set out toward the crest of the hill country, saying, “We are prepared to go up to the place that ה׳ has spoken of, for we were wrong.” (41) But Moses said, “Why do you transgress יהוה’s command? This will not succeed. (42) Do not go up, lest you be routed by your enemies, for ה׳ is not in your midst. (43) For the Amalekites and the Canaanites will be there to face you, and you will fall by the sword, inasmuch as you have turned from following ה׳ and ה׳ will not be with you.”

(44) Yet defiantly they marched toward the crest of the hill country, though neither יהוה’s Ark of the Covenant nor Moses stirred from the camp.

(45) And the Amalekites and the Canaanites who dwelt in that hill country came down and dealt them a shattering blow at Hormah.

Another interpretation, “you will utter a decree ” – Rabbi Yehoshua of Sikhnin said in the name of Rabbi Levi: Everything that Moses decreed, the Holy One blessed be He agreed with him. How is this so?

The Holy One blessed be He told him to wage war with Siḥon, as it is stated: “Provoke war against him” (Deuteronomy 2:24). But he did not do so. Instead, “I sent messengers [from the wilderness of Kedemot to Siḥon, king of Ḥeshbon, with words of peace]” (Deuteronomy 2:26). The Holy One blessed be He said to him: ‘This is what I said to you, to wage war against him, but you started off with an offer of peace. By your life, I will fulfill your decree: Every war that they wage, they shall start off only with an offer of peace,’ as it is stated: “When you approach a city…”

(1) A king should not wage other wars before a milchemet mitzvah. What is considered as milchemet mitzvah? The war against the seven nations who occupied Eretz Yisrael, the war against Amalek, and a war fought to assist Israel from an enemy which attacks them.
Afterwards, he may wage a milchemet hareshut, i.e. a war fought with other nations in order to expand the borders of Israel or magnify its greatness and reputation.

(2) There is no need to seek the permission of the court to wage a milchemet mitzvah. Rather, he may go out on his own volition and force the nation to go out with him. In contrast, he may not lead the nation out to wage a milchemat hareshut unless the court of seventy one judges approves.

(16) In the towns of the latter peoples, however, which your God ה׳ is giving you as a heritage, you shall not let a soul remain alive. (17) No, you must proscribe them—the Hittites and the Amorites, the Canaanites and the Perizzites, the Hivites and the Jebusites—as your God ה׳ has commanded you, (18) lest they lead you into doing all the abhorrent things that they have done for their gods and you stand guilty before your God ה׳.

Rabbi Menahem ben Meir (Meiri), in his commentary on the Talmud," states that an Authorized war is any attack that is commenced in order to prevent an attack in the future. Once hostilities begin, all military activity falls under the rubric of Obligatory. Similarly, Rabbi Abraham Isaiah Karelitz (Hazon Ish) claims that Maimonides’ definition of an Authorized war is referring to a use of force in a war of attrition situation. In any circumstance in which prior "battle" has occurred and that battle was initiated by the enemy, the war that is being fought is an Obligatory one. According to this approach, the use of military force prior to the start of a war of attrition is prohibited (unless justified by the general rules of self-defense, in which case a "war" is not being fought according to Jewish law.)

See: The Bounds of Wartime Military Conduct in Jewish Law: An Expansive Conception Michael J. Broyde

Rabbi Yosei HaGelili said: How meritorious is peace? Even in a time of war, Jewish law requires that one initiate discussions of peace. That is what is written: “When you approach a city to wage war against it, [you shall call to it for peace]” (Deuteronomy 20:10).