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Voluntary war (Hebrew: מלחמת הרשות; milḥemet ha-reshūt), sometimes called a discretionary war, optional war, a non-obligatory war, or a war of free choice, is a technical term found in Hebrew classical literature and denoting a war that is waged of free choice by Israel, only at such a time when the people of Israel are settled in their ancestral homeland. Such a war cannot be waged without either the approbation of the Great Sanhedrin, consisting of no fewer than seventy-one judges, or, according to some authorities, without the command of a king.

The Hebrew Bible assumes war as inevitable when it says, "When you go out to war against your enemies" (Deut. 20:1).^[1] It has often been cited and used as the constitutional basis for traditional laws of conquest, where the defeated are either killed or enslaved.^[2] Traditional Jewish law recognizes as a category of permissible war, wars undertaken in order "to diminish the heathens so that they shall not march against them."^[3] The earliest age given in the Hebrew Bible for military conscript is age twenty.^[4] Old men (aged 60), as well as the lame and the blind, are exempt from military service.^[5]

King David waged a voluntary war against the Moabites and the Ammonites (2 Samuel 8 and 1 Chronicles 19),^[6][7] and also against the inhabitants of Aram Zobah.^[8][7] In the case of Moab and Ammon, some commentaries hold these to be voluntary wars spurred-on by revenge, because they had attacked Israel.^[9]

In 164 BCE, Mattathias, the progenitor of the Hasmonean dynasty, made it a law that it was permissible for Jews to defend themselves on the Sabbath day, even if it meant desecrating the Sabbath, when attacked by their enemies.^[10] His son, Judas Maccabeus, when trying to curtail the advances of the enemy Syrian troops who had invaded the country, put into practice the teachings of Moses, as prescribed in the 'ancient order of battle' (Deut. 20:1–ff.), and dismissed from his army those men who had recently been married to a wife.^[11]

The great rabbis and sages of Israel distinguish between a voluntary war and a mandatory war. A voluntary war is not fought for national survival, but rather for personal ambitions of the country's ruler. This might include personal enmity with another state, or a desire to show the country's military prowess as a means to deter potential aggressors, or to expand the territorial domain of the country.^[12] A voluntary war may only be waged by authorization of the greater Sanhedrin, composed of seventy-one judges,^[13] presumably in order to impose a religious and moral check on reckless warfare.^[14] Other authorities also permit a king to initiate a war, since a king is the supreme commander of the army.^[15][16][a] In other respects, a voluntary war is to be distinguished from a religious war, insofar that a religious war concerns the conquest of the land of Canaan by Joshua.^[17]

For all practical purposes, a voluntary war can be described as an offensive war, but in the absence of either a monarchy or the Sanhedrin such a war is lacking in its powers and in its authority to be waged, and there is no man who can forcibly be taken to join the war effort.^[18][19] Moreover, a voluntary war can only be waged by Israel when the people are settled in the Land of Israel.^[20] Such laws do not apply to Jews serving in foreign armies.

The early Sages of Israel mitigated the laws of armed conflict. In the case of a voluntary war, it was bound by certain legal constraints and restrictions (jus in bello), inasmuch as it was prohibited by halakha to wage a voluntary war on the Sabbath day, unless it were to save life.^[21] Moreover, according to the Babylonian Talmud, Shabbat 19a, in a war waged of free choice, whenever Israel lays siege to a city belonging to the enemy, the siege must be initiated at least three days before the start of the Sabbath,^[22][b] and it is incumbent upon Israel to offer the besieged conditions of capitulation (peace), such as the guarantee of their lives being spared if they agree to be put under tribute and servitude to the Jewish nation,^[25] and on condition that they agree to observe the seven basic commandments given to the sons of Noah.^[26] For this, embassages and heralds are sent to representatives of those persons who make themselves voluntary enemies to the nation of Israel in order to extend conditions of peace.^[27] Once the siege has begun, war is made against the besieged city and continues thereafter, day after day, even on the Sabbath day itself, as it says: "until it be subdued" (Deut. 20:20).^[28][29]

In a voluntary war, not all able-bodied men are conscripted to fight, as there are certain exemptions outlined explicitly in the Torah, namely:

1. 'the one who built a house and did not dwell in it a year's time'^[30][c]
2. he that 'planted a vineyard and did not partake of its fruit'^[32]
3. the one who has 'betrothed a wife and has yet to perform his marital duty' on her.^[33]
4. the one who is 'fearful and faint-hearted'.^[34][35]
5. the one whose conscience bothers him because of having committed certain sins.^[36]

Formerly, in Jewish halachic law, it was incumbent upon a priest descended from Aaron's lineage and who had been specifically tasked with the vetting process to officiate over the conscription of new recruits (משוח מלחמה‎; the anointed for battle), to announce unto the people the legal requirements and to screen those who were exempt from military service, while admonishing and encouraging all others, in the Hebrew language, to fight valiantly.^[37][38][39] This priest was to be anointed with the holy anointing oil.^[40] He was assigned Levite officers who were themselves priests to assist him in conveying these messages in an audible voice to the people, immediately prior to engaging in battle.^[41] Afterwards, captains were appointed over the soldiers to conduct the war, and to take-up positions at the fore of the battle, as well as at the rearward of military operations.^[42][43]

Soldiers are prohibited from defecating in the open field, in such a way that their waste remains visible, but must carry with them a trowel-like implement needed to dig a hole in a pre-designated place and to cover-up their excreta after relieving themselves.^[43] If, in the course of the voluntary war, soldiers were recalled from active duty (although they did not fall under the category of those who had newly wedded a wife, neither those who had built a new house, nor planted a vineyard), they would be commissioned by the acting officers to fix the public roads, to provide food and water on the war behalf, in addition to being assessed for the town tax.^[44][d] Such duties and responsibilities do not apply to the man who is newly wedded, or who has built a new house or planted a vineyard, as he is exempt from all these.^[45][e]

In Jewish halachic law, it is forbidden to lay siege to a city by completely closing-off the city on all four sides. Rather, a besieged city must be encompassed only on its three sides, to enable those who wish to escape to escape.^[46] Moreover, it is prohibited under Jewish law to cut down the fruit trees of a besieged city while maintaining the siege, in order to punish the people of the besieged city (Deuteronomy 20:19-20), although it is permitted to cut-down trees that do not bear fruit, to be used in the siege.^[47] Neither is it permissible for the warring party that lays siege to a city to prevent from its inhabitants water that is being channeled into the city via an aqueduct.^[43] In those cities where the besieged people refuse to capitulate and to make peace with Israel, the Torah sanctions the killing of all males of warring age in that city, but the women, small children and livestock are to be taken as legal plunder.^[48][49]

Conscripted soldiers taking part in the voluntary war effort have been given special privileges to make fighting easier for them, or else to keep them blameless:

1. If, in the course of the war, a Jewish man sees a beautiful gentile woman among the captives, whether she is a single woman or a woman married to another man, and his passions are aroused by her beauty and he desires to lay with her carnally (being unable to control his passions), he may conscionably do so, without guilt, when his intent is to marry her,^[50] since the Torah has condoned his actions during the time of warfare.^[51][g]
2. Soldiers taking part in the war effort are permitted to purloin any dry wood for their personal use.^[56][h]
3. Soldiers taking part in the war effort, in the event of food scarcity, are permitted to eat of animals that have been improperly butchered, and even to feast on the 'necks of swine' (Hagigah 17a).^[57]
4. Soldiers taking part in the war effort are permitted to return to their places with their weapons in hand, even on a Sabbath day.^[58]
5. Soldiers taking part in the war effort are exempt from hand washing immediately prior to eating bread, since this would be an encumbrance upon them.^[43][59]
6. Soldiers taking part in the war effort are permitted to eat of fruits and vegetables that have the status of Demai-produce.^[43][59]
7. Soldiers taking part in the war effort are exempt from observing the laws governing the extension of courtyards (ʻerūvei ḥaṣerot) on the Sabbath day (Eruvin 17a–b).^[60]
8. A soldier killed in battle may be buried in the place where he had fallen, even if his family members were known and they could retrieve the body and take it to their private family's burial plot (Eruvin 17a–b).^[61]

According to the Bayit Chadash, notwithstanding the lack of conditions which would otherwise make a voluntary war valid today, Jewish men may still find themselves serving as soldiers in non-Jewish armies among the nations of the world. In which case, Jewish soldiers who are called to lay siege to a city, unlike their regular non-Jewish unit or regiment, are still obligated to abide by the strictures outlined in rabbinic writings and must embark on the siege with at least three days in advance of the Sabbath-day.^[62] Moreover, if there was a case whereby Jews and Gentiles had been taken captive by enemy forces, it is permissible for Jewish soldiers serving in foreign armies to set-out to rescue the captives, even on a Sabbath-day, since the saving of Jewish life takes precedence over the Sabbath-day, and is withal tantamount to a religious war.^[62]

• Armed conflict
• Declaration of war
• Hegemony
• Judaism and warfare
• Jus ad bellum
• Just war theory
• Law of war
• Laws of armed conflict
• Military justice

• Broyde, Michael J. (2007). "Just Wars, Just Battles, and Just Conduct in Jewish Law: Jewish Law is Not a Suicide Pact!". In Schiffman, Lawrence; Wolowelsky, Joel B. (eds.). War and Peace in the Jewish Tradition. New York: Michael Scharf Publication Trust of the Yeshiva University Press; Distributed by KTAV Pub. House, New York. pp. 2–3. ISBN 9780881259452. OCLC 76792033.
• Waldenberg, Eliezer Y. (1952). Sefer Hilkhot Medinah (in Hebrew). Vol. 2. Jerusalem: Mossad Harav Kook. p. 119 (chapter: milḥemet reshut). OCLC 253782196.