The discontinuance of the practice of cannibalism--the practice seems invariably to be left behind by all peoples as soon as they have made any considerable advance in civilization[60]--may with little hesitation be attributed in part at least to the growth and refinement of the moral feelings. In one case at least we have historical evidence that among a wide reach of savage tribes the custom was abolished by the action of a more civilized people, who did just what the more advanced European nations, under the impulsion of moral feeling, are doing in regard to the slave trade and cannibalism in Africa to-day. The Incas of Peru, before granting to conquered tribes terms of peace, forced them to abandon the practice of cannibalism.[61] The disuse of poisoned arrows marks another significant mitigation of a common barbarity of early warfare. We know that in the Greek world by the opening of the historic period there were communities that had come to look on the use of poisoned weapons with abhorrence, and to regard the practice as a crime that aroused the anger of the gods. Thus Homer represents Ilus of Ephyra, when asked by Odysseus for the fatal poison wherewith to smear the tips of his arrows, as refusing his request because he feared the immortal gods.[62] In these mitigations and prohibitions of the barbarities of war on the lower levels of savagery we have probably the earliest articles of the war code of the nations. They mark the first steps taken in the humanization of war. They indicate the birth of those sympathetic and moral feelings which, though of painfully slow growth and of intermittent action, have during the course of the historic ages effected great ameliorations of the cruelties of primitive warfare, and foreshadow a time when war between civilized nations shall have become an inconceivable thing. [Sidenote: The reaction of intertribal upon intratribal morality] There is a heart of good in things evil. Even the habitual intertribal wars of primitive communities contain a germ of good. The pressure exerted by these life-and-death struggles upon the clan or tribe has a good effect upon the inner relationships of the group. Many of the social virtues, such as loyalty to comrades and self-devotion to the common weal, are called into constant and keen activity. For this reason we usually find these social virtues well developed among peoples in the clan or tribal stage of civilization. Such peoples may even be stronger in these special virtues than civilized peoples.