The ethic of war has been always of special importance for the scholars of the field. In this paper, the common views of western philosophers have been surveyed and then, using Quranic verses and traditions, the view of Islam on ethical justifiability of initial holy war has been explained, and some questions in the field have been answered. As legality of holy war in Islam has been based upon monotheism and justice, the prerequisite for it lies in its being for the sake of God`s will. On the very state of holy war, the important objection of western philosophers can be replied. For Islam, initial war is conditioned with a lot of requisites including facing invasion, supporting the cruel, opposing devilry, lacking of peaceful way