Many scholars describe Augustine as the ‘‘father’’ of Christian just war thinking. Given his great legacy in this, as in other areas of political thought, there is some reason for such a characterization. Nevertheless, as noted above, Augustine’s notions of war build on several centuries of development. In particular, Ambrose’s combination of biblical and Roman ideas of bellum iustum provides a context in which Augustine’s ideas make sense.
Also, Augustine never provides a succinct, systematic statement of just war criteria. Instead, his judgments are sprinkled throughout his works, especially The City of God. A far more systematic statement is found in the Summa theologiae of Thomas Aquinas (d. 1274). At Ilallae, q. 40, Thomas asks whether it is always a sin to wage war. In response, he writes that there are three things required for a war to be just. First, the war must be commanded by a prince who possesses the authority to make war. Second, the war must be fought for a just cause; showing his debt to Augustine, Thomas indicates that this usually implies a war fought to avenge injuries, for example, when a state deserves to be punished for failing to restore things unjustly taken or to right wrongs done by its people. The third requirement is right intention, and again Thomas quotes Augustine with respect to those evil dispositions, which may be described as the ‘‘real’’ evils associated with war.
As noted, Thomas built on Augustine. He references a number of other sources, however, and thus points to the continuing development of Christian just war thinking.
By Thomas’ time, the efforts of ecclesiastical and political leaders to limit war by such conventions as the Peace of God and the Truce of God (tenth and eleventh centuries) were well-entrenched. In particular, the former forbade direct and intentional attacks on specific targets. These included churches, as well as certain classes of people whose age, gender, or vocation would normally identify them as nonparticipants in fighting. The latter tried to prohibit fighting on specific days, at least among Christians. The influence of both efforts are evident in Thomas, as he addresses questions regarding the participation of clergy in fighting (he says it is not normally allowed, because it does not fit with their vocation) and of the possibility that fighting may be prohibited in certain times and places.
Most notably, though, Thomas’ statement of just war criteria presupposes developments in canon law. The influence of Gratian’s Decretum (mid-twelfth century), as well as of the various commentators on that work and on the Decretals, is particularly evident in the first of Thomas’ concerns. From the late ninth century, the collapse of the Carolingian Empire provided a context in which various authorities competed for power, and in which the incidence of fighting among Christians became a cause of concern. As the canon lawyers (and Thomas) had it, only a prince possessed competence de guerre; and a prince, in their vocabulary, meant a ruler whose control of a particular territory indicated that he had no superior. Such a ruler could be recognized by the Pope, who as the vicar of Christ was responsible for the moral and spiritual welfare of Christians. When Urban II appealed to Christians in 1095 to join in a Crusade against the Seljuk Turks, he did so particularly with reference to those princes whose sphere of power qualified them as authorities, in Thomas’ sense.
Right authority thus constituted the most important area in which Thomas’ statement indicates the influence of canon law. As with the canonists, however, the summary of Thomas leaves a certain ambiguity. If those who possess authority with respect to war do so in part because of ecclesiastical recognition, where does authority actually rest? Is it with those secular authorities described as princes? Or with the Pope, who recognizes and, in the instance of the Crusades, summons the princes to organize their armies for a particular fight? In dealing with the topic of war, Thomas seems to say that the princes possess authority for war and that ecclesiastical authorities only direct and exhort them in the exercise of that authority. And yet, the authority of the church does involve an evaluation of the legitimacy of secular rulers. Particularly with respect to fighting against the Turks, or to Christendom’s internal fight against heretics, the Pope’s authority seems paramount. As succeeding generations would have it, the ‘‘just war’’ allowed for a distinction between two sorts of causes, and the role of secular and ecclesiastical authorities differed as one considered this distinction. Thus, secular authorities might authorize fighting for the common good, construed in terms of recovery of territory or goods taken through aggression. By contrast, fighting for a religious cause - here, Thomas’ reference to Augustine’s notion that the ‘‘injury’’ justifying war might involve punishment for wrongs done could be extended to include idolatry and other matters of religion - should be authorized by the Pope, and Christian rulers did their duty by responding to his call.
Interestingly, Thomas’ own position on the war against the Turks shows considerable nuance. He is not convinced that fighting Muslims in order to punish their religious errors is justified, and seems to prefer to refer such fighting to notions of a right of passage. All people, including Christians making pilgrimage to Jerusalem, have a right to travel peacefully. If Muslim authorities restrict that right, there may be a just cause of war against them. Such a cause might even justify taking back the lands conquered by Muslims, a rationale further supported by the notion that territory taken by aggression may be recovered through military force. Even here, though, Thomas’ argument shows nuance, since he wonders whether retaking territory after a long occupation may not upset established patterns of living, and thus do more harm than good.
Where Thomas does suggest that religion presents a just cause of war is in matters of heresy and blasphemy. It is not right to fight against unbelievers, for example Jews, in order to compel their faith. But it is right to fight against those who claim to be Christians, but dissent from the teaching of the church. The latter case involves the breaking of a contract with God; it is the church’s right and duty to punish such wrongdoing, and to provide an example to others who might be tempted to part ways with the church.
In all these matters, Thomas and others involved in the just war discussion addressed issues which vexed morally sensitive souls throughout the Middle Ages. Augustine’s writings on the Donatist controversy provided an early example of the tensions built into the connection of just war with wars fought on behalf of religion. Given instances in which the latter could be connected with disproportionate force, or even with massacre, the notion of fighting for religious causes was gradually separated from the more clearly political causes for which secular rulers possessed authority. At the close of our period, Francisco de Vitoria could evaluate the claim of the Spanish emperor with respect to fighting against the indigenous peoples of the New World in such a way as to suggest that difference of religion, in and of itself, could never provide a just cause of war. Nor could the emperor authorize fighting based on a claim that dominion over the natives’ lands had been granted him by the Pope. The Pope’s authority with respect to the New World extended only to the matter of sending missionaries who would preach the Gospel. Should the natives refuse passage to these envoys, and particularly if they should kill or otherwise harm them, then a limited use of military force might be justified. But just wars have to do with limited, political causes, and secular authorities show their good intention by understanding that limited causes require limits on means - in other words, the conduct of war provides an important measure of the justice of the various sides.
World History
