<P> The historical aspect, or the "just war tradition", deals with the historical body of rules or agreements that have applied in various wars across the ages . The just war tradition also considers the writings of various philosophers and lawyers through history, and examines both their philosophical visions of war's ethical limits and whether their thoughts have contributed to the body of conventions that have evolved to guide war and warfare . </P> <P> The Indian Hindu epic, the Mahabharata, offers one of the first written discussions of a "just war" (dharma - yuddha or "righteous war"). In it, one of five ruling brothers asks if the suffering caused by war can ever be justified, and then a long discussion ensues between the siblings, establishing criteria like proportionality (chariots cannot attack cavalry, only other chariots; no attacking people in distress), just means (no poisoned or barbed arrows), just cause (no attacking out of rage), and fair treatment of captives and the wounded . The war in the Mahabharata is preceded by context that develops the "just cause" for the war including last minute efforts to reconcile differences to avoid war . At the beginning of the war, there is the discussion of "just conduct" appropriate to the context of war . </P> <P> A 2017 study found that the just war tradition can be traced as far back as to Ancient Egypt, "demonstrating that just war thought developed beyond the boundaries of Europe and existed many centuries earlier than the advent of Christianity or even the emergence of Greco - Roman doctrine ." </P> <P> In ancient Rome, a "just cause" for war might include the necessity of repelling an invasion, or retaliation for pillaging or a breach of treaty . War was always potentially nefas ("wrong, forbidden"), and risked religious pollution and divine disfavor . A "just war" (bellum iustum) thus required a ritualized declaration by the fetial priests . More broadly, conventions of war and treaty - making were part of the ius gentium, the "law of nations", the customary moral obligations regarded as innate and universal to human beings . The quintessential explanation of Just War theory in the ancient world is found in Cicero's De Officiis, Book 1, sections 1.11. 33--1.13. 41 </P>

All of the following have historically been considered causes of world war i except