Armies of the caliber of Rome’s were often able to do what they should not have

From Carnage and Culture by Victor Davis Hanson. Page 130.

Civic militarism itself would not always ensure numerical superiority for Western armies – the manpower pool of Europe and its colonies would often turn out to be inferior to that of Asia, Africa, and the Americas. Nor would a nation-in-arms always be guaranteed victory through greater morale. At times Christianity would prove that the Sermon on the Mount is a less effective incentive for warriors than jihad. Moreover, Western armies that ventured abroad and across the sea would often be small, professional, and on occasion mercenary. Nevertheless, the ideal of a collective defense by its free citizenry — the musters of the Franks, the pikes of Switzerland, sailors of Venice, or yeomen of England and France — would help to ensure that for most of the time post-Roman Europe itself was safe from invasion, and its overseas expeditionary troops trained, organized, and led with a zeal that emanated from beyond a narrow aristocratic caste — and were thereby more than a match for the numbers and the skill of their non-Western adversaries.

Again, the latter were sometimes braver men. On occasion they fought for a better cause than the Westerners who invaded their country, ruthlessly enslaved their people, slaughtered women and children, and looted their treasure. The study of military dynamism is not necessarily an investigation into morality — armies of the caliber of Rome’s were often able to do what they should not have. Civic militarism ensured large and spirited armies, not necessarily forces that would respect the cultural and national aspirations of others and the sanctity of human life in general. In that narrow regard of military efficacy, no other people on a single occasion—not Persians, Chinese, Carthaginians, Indians, Turks, Arabs, Africans, or Native Americans—would ever march as free citizens with abstract conceptions of civic rights, and at the formal direction of an elected assembly, but were more commonly paid, frightened, or mesmerized into service to a chief, sultan, emperor, or god. In the end, that fact in and of itself often proved a disadvantage on the battlefield. Sadly, the Western method of creating public armies and legal terms of service was not necessarily a question of good or evil, fairness or injustice, right versus wrong, but one of military skill.