The Torah instructs that before waging war the enemy should first be offered the opportunity to surrender peacefully. Rashi writes that this option is only given during a milchemes reshus, but not a milchemes miztva, such as the battle against Amalek or the other 7 nations living in Eretz Yisrael. Ramban and Rambam (Hil Melachim ch 6) disagree and write that this choice is always offered. Any nation, even Amalek, which accepts the 7 Noahide commandments and agrees to pay taxes and Jewish dominion can peacefully surrender and avoid war. The Rambam (see also Tosfos Sota 34b) writes that before Yehoshua began his wars in Eretz Yisrael he sent letters to the nations living there offering them the option of peaceful surrender, fleeing the land, and a warning that otherwise he would wage war.
Commenting on the Rambam’s position that even Amalek and the 7 nations may sue for peace by accepting servitude, taxes, and the 7 Noahide laws, the Ra’avad writes “zeh shibush, elah sheyachol lomar hashlimu l’kabeil mitzvos” – “the Rambam is in error, as they can say make peace by accepting the mitzvos.” The comment of the Ra’avad is very difficult to understand – the Rambam himself acknowledges that accepting the 7 Noahide mitzvos is a prerequisite for peace?
Most (see Radbaz, KS”M, Minchas Chinuch) interpret the Ra’avad as amplifying his own position. Ra’avad earlier writes that all nations other than the 7 of Eretz Yisrael and Amalek may sue for peace by accepting Jewish dominion and the obligation to pay taxes without the accepting the Noahide laws. The Ra’avad here makes clear that with respect to the 7 nations of Eretz Yisrael and Amalek more is needed – they must accept the 7 Noahide laws as well. The problem with this reading is it does not seem to explain what the Ra’avad objected to in the Rambam’s position other than perhaps his syntax.
The Chazon Ish (Y.D. 157:5) offers a brilliant explanation of this Ra’avad that seems to fit the words exactly. The Ra’avad thought the Rambam mistaken in saying the 7 Nations and Amalek are extended an offer of peace. However, Ra'avad agrees that these nations may voluntarily come forward and sue for peace based on their acceptance of the 7 Noahide laws. “Sheyachol lomar hashlimu l’kabeil mitzvos” – the 7 Nations can say of their own accord that they desire peace and accept the 7 Noahide mitzvos, and only under those terms can they be spared.