The Torah commands in Parashat Shoftim (Debarim 20:10-15) that when Beneh Yisrael plan to wage war against an enemy nation, they must offer the nation peace. If the nation agrees to serve Beneh Yisrael and pay them a tax, then Beneh Yisrael must deal with them peacefully, and may not wage war against them. If the nation refuses, then Beneh Yisrael are to fight and kill all the men.
The Sages understood that these verses refer to a situation of “Milhemet Reshut” (“optional war”), meaning, a war which is not obligatory according to Torah law. When it comes to a “Milhemet Misva” – a war which Beneh Yisrael are obligated to wage – the rules are different. Examples of a “Milhemet Misva” are the battles against the seven nations of Canaan, and the battle against the evil nation of Amalek. The Sefer Ha’hinuch writes that even with regard to these nations, Beneh Yisrael must first offer peace, and if the nation accepts, then Beneh Yisrael must not fight against them. If the nation refuses, however, then Beneh Yisrael must kill the entire nation, including the women and children. This is one difference between a “Milhemet Reshut” and a “Milhemet Misva” – that in the former case, the women and children are spared, whereas in the latter case, there aren’t. Another difference between these two kinds of wars is that during a “Milhemet Reshut,” the soldiers may not surround the enemy army on all four sides; they must allow them an escape route. During a “Milhemet Misva,” by contrast, there is no such requirement, and Beneh Yisrael’s army surrounds the enemy troops on all four sides.
The Sefer Ha’hinuch explains that the Torah commands offering peace before going to war because of the great importance of the quality of Rahamanut – mercy and compassion toward others. We, G-d’s sacred nation, are expected to conduct ourselves mercifully in all our dealings with other people, even when waging war against pagan nations. Additionally, the Sefer Ha’hinuch writes, waging war unnecessarily, even against evil nations, gives the appearance of cruelty, and, moreover, denies Beneh Yisrael the benefit of these nations’ service and tax money.
During both a “Milhemet Reshut” and a “Milhemet Misva,” if the soldiers do not have access to kosher food, they are permitted to eat even non-kosher food.
This Misva applies only when the Jewish Nation resides in its land, and it is binding upon the king or other leaders who have the power to enforce these laws. If the king did not first offer peace before initiating a “Milhemet Misva,” he has violated this affirmative command.