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What Is the Definition of a Milchemes Mitzvah and a Milchemes Reshus?

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In the Torah, war is not a secular or nationalistic decision — it is a halachic matter, with clear categories and conditions defined by Chazal and the Rishonim. The Rambam famously distinguishes between two kinds of wars in Hilchos Melachim (Laws of Kings and Wars): Milchemes Mitzvah (a commanded war) and Milchemes Reshus (a discretionary war).

1. Milchemes Mitzvah – A War of Obligation

A milchemes mitzvah is a war that is a Torah obligation, falling under the direct command of Hashem or defined by halacha as necessary for the survival and spiritual mission of Klal Yisrael. There are several types:

a. Defensive Wars

Any war fought to protect Jewish lives from an attacking enemy is a milchemes mitzvah.

“To assist Israel against an enemy that attacks them, this is a milchemes mitzvah.” — Rambam, Hilchos Melachim 5:1

b. The Conquest of Eretz Yisrael (in the days of Yehoshua)

The initial conquest of the Land of Israel was a direct Divine commandment to the nation.

“The war of Yehoshua to conquer the Land — that is a milchemes mitzvah.” — Rambam, ibid.

c. Destroying Amalek

The command to destroy Amalek (Shemos 17, Devarim 25) is a mitzvah that obligates all generations when the conditions are met.

“Three mitzvos were commanded to Israel upon entering the Land: to appoint a king, to destroy Amalek, and to build the Beis HaMikdash.” — Sanhedrin 20b

2. Milchemes Reshus – A Discretionary War

A milchemes reshus is a war not required by halacha but permitted under certain Torah-sanctioned circumstances. These include wars waged for:

  • National expansion
  • Strategic advantage
  • Political stability

However, such wars were subject to strict conditions:

  • Only a king could declare it.
  • He needed approval from the Sanhedrin of 71.
  • He also required a message from the Urim v’Tumim — Divine guidance through the Kohen Gadol's breastplate.

“A king does not go to war [a milchemes reshus] unless it is with the counsel of the Sanhedrin of 71 and the word of the Urim v’Tumim.” — Rambam, Hilchos Melachim 5:2

Because of these conditions, such wars could only be waged during the times of full Torah governance — with a righteous Jewish king, Sanhedrin, and prophetic guidance.

Sources & Footnotes

  1. Rambam, Hilchos Melachim uMilchamos 5:1–2
  2. Sanhedrin 20b
  3. Ramban, commentary to Sefer HaMitzvos, Shoresh 3 and Mitzvas Asei 4
  4. Rashi on Devarim 20:1, regarding war types
  5. Sefer HaChinuch, Mitzvah 425
  6. Tosfos, Sanhedrin 2a, and Kesubos 15b
  7. Minchas Chinuch on Mitzvah 425