Socrates in the Republic (V. 469, 470) gives expression to a feeling which was gradually gaining ground in Greece, that war between Hellenic tribes was much more serious than war between Greeks and barbarians. In such civil warfare, he considered, the defeated ought not to be reduced to slavery, nor the slain despoiled, nor Hellenic territory devastated. For any difference between Greek and Greek is to “be regarded by them as discord only—a quarrel among friends, which is not to be called war”.... “Our citizens [i.e. in the ideal republic] should thus deal with their Hellenic enemies; and with barbarians as the Hellenes now deal with one another.” (V. 471.)
The views of Plato and Aristotle on this and other questions were in advance of the custom and practice of their time.
[9] “The Lord is a man of war,” said Moses (Exodus XV. 3). Cf. Psalms XXIV. 8. He is “mighty in battle.”
[10] This was bound up with the very essence of Islam; the devout Mussulman could suffer the existence of no unbeliever. Tolerance or indifference was an attitude which his faith made impossible. “When ye encounter the unbelievers,” quoth the prophet (Koran, ch. 47), “strike off their heads, until ye have made a great slaughter among them.... Verily if God pleased he could take vengeance on them without your assistance; but he commandeth you to fight his battles.”
The propagation of the faith by the sword was not only commanded by the Mohammedan religion: it was that religion itself.
[11] See Acts X. 28:—“Ye know that it is an unlawful thing for a man that is a Jew to keep company, or come unto one of another nation.”
[12] Neither, however, is there any which regards the soldier as a murderer.
[13] In the early centuries of our era Christians seem to have occasionally refused to serve in the army from religious scruples. But soldiers were not always required to change their profession after baptism. And in Acts X., for example, nothing is said to indicate that the centurion, Cornelius, would have to leave the Roman army. See Tertullian: De Corona (Anti-Nicene Christian Library), p. 348.
[14] There were so-called “Sacred Wars” in Greece, but these were due mainly to disputes caused by the Amphictyonic League. They were not religious, in the sense in which we apply the epithet to the Thirty Years’ war.
[15] “The administration of justice among rude illiterate people, was not so accurate, or decisive, or uniform, as to induce men to submit implicitly to its determinations. Every offended baron buckled on his armour, and sought redress at the head of his vassals. His adversary met him in like hostile array. Neither of them appealed to impotent laws which could afford them no protection. Neither of them would submit points, in which their honour and their passions were warmly interested, to the slow determination of a judicial inquiry. Both trusted to their swords for the decision of the contest.” Robertson’s History of Charles V., (Works, vol. V.) Sect. I., p. 38.