In the Fall of 2021 I gave an invited lecture to a class on strategy at the Australian equivalent of the United States war colleges. The members of the class were army, air force, and marine colonels as well as naval captains. My topic was assigned: Just War and the Future of War. I discussed both the war-decision and war-fighting aspects of the just war idea (the jus ad bellum and the jus in bello), sketching their historical development, current status, and relationship to the efforts to regulate war in international law. Turning to the application of just war thinking to the future of war, I focused on what had become the pattern of warfare in the decades since the end of World War II. Several decades ago it was thought that the future of war would be an imagined “World War III,” reprising World War II’s all-out clash of major-power militaries that would escalate to the use of nuclear weapons, history has unfolded differently. Instead, we have seen relatively small regional wars, insurgencies, and wars resulting from terrorist activity in which great powers and their militaries have been involved only peripherally or not at all and certainly not in such ways as to escalate into great-power conflict. I noted that most observers and military planners anticipated the continuation of the small war/insurgency/terrorism model, so I was hardly alone in my expectation.
Then, of course, the world changed: Russia invaded Ukraine, using tactics and weaponry that brought back memories of the Red Army’s tactics in World War II and which NATO forces expected to meet in the Fulda Gap during the tensest years of the Cold War. Only weeks after the invasion of Ukraine came another crisis involving the military forces of a major power when China responded to US House Speaker Nancy Pelosi’s visit to Taiwan with a heavy commitment of naval vessels to blockade Taiwan’s ports, numerous aerial sorties near and over Taiwan, rocket launches over and around the island, and a buildup of land forces on the Chinese mainland along the Taiwan Strait. Neither the Russian nor the Chinese actions amounted to the imagined “World War III,” but they corrected the “small war” model and served as a reminder that both Russia and China, besides being nuclear powers, had both undertaken to reform and build up their military forces during previous decades.
What might this mean for the impact of just war thinking on the developing face of war? The answers are different for each case.
Just war thinking itself is a synthesis of ideas that emerged and came together in Western culture over a long history. Despite the idea of just war has ancient, classical and Hebraic roots it has often been described as beginning with the thought of the Christian St. Augustine of Hippo in the fifth century CE. This characterization goes too far: though Augustine was indeed an important figure for the development of the tradition of just war, he never produced a systematic work on it. His influence as a just war theorist arises from a number of brief passages dealing with various just war issues found in a broad range of works on different topics. Beginning in the sixth century, these scattered passages were identified and collected by a series of canon lawyers as a guide for Christian living and particularly to identify sinful activity in the context of the sacrament of penance. The word “canon,” brought over into Latin from the Greek, means “rule” or “law,” and the early medieval canonical collections included both formal canons issued by councils of bishops and passages from the works of Christian authorities, including Augustine, that thus took on the same status as guidance for Christian life. These medieval canonical collections, circulated among the priests in Western European dioceses and passed down from generation to generation, provided a basis for both pastoral teaching and religious discipline among a largely illiterate Christian laity. This legal system would guide Christian Europe from the fall of the Roman Empire to the rise of societies ruled chivalric elites, both in temporal politics and in the Church.
The canonical collections from the sixth through the early twelfth centuries were not, however, systematically organized. Though the passages drawn from Augustine on right behavior in relation to war were especially relevant to the concerns of the chivalric class, as they bore not only on warfare but also on the exercise of temporal government, they were not connected into a systematic body of thought on just war. This was corrected by the canonist Gratian in his mid-twelfth century text Decretum. In this work, together with that of the two generations of commentators that annotated and expanded the scope of the Decretum, that the just war idea in its classic form first took shape. The focus of Decretum was fundamentally on the justice of making war, with the contours of this idea eventually summarized and placed into theological context by Thomas Aquinas in his Summa Theologiae at the end of the thirteenth century. Aquinas described just war as a use of armed force by a sovereign authority for a just cause (a response to an act or threat of injustice) and with a right intention defined both by a list of wrong intentions drawn up by Augustine as always to be avoided and by an overall intention to establish or preserve peace. By the time of Aquinas these basic ideas had become embedded in both the Church’s canon law as well as in chivalric culture. Moreover, in both they were understood as grounded in natural law and central to the exercise of good government by sovereign rulers. That is, though the canonists and Aquinas worked in a churchly frame, the just war idea they produced was not rooted in Christian doctrine but rather was a spelling out of natural law in the service of government in the name of the common good and overall justice and peace. The temporal nature of this conception of just war was expanded later, in the era of the Hundred Years War, by the incorporation of the chivalric code of conduct in warfare alongside the canon law list of persons who, during war, deserved not to be attacked because of their age, gender, or occupation. From this historical point on the idea of just war included both its jus ad bellum and its jus in bello. This filled out the full shape of the classic idea of just war, eventually passing into the modern era through the work of Grotius and others, thus providing a basis for the the modern idea of the law of nations. As Europe progressed into the modern age, just war provided both a focus for the conduct of statecraft and a body of rules to be observed in armed conflict. By the 1800s this body of rules for the conduct of war was referred to as “the laws and customs of war,” which in turn provided the foundation from which international laws of war developed in the modern sense of formal agreements among nations by which they pledged to behave in certain ways and to seek to enforce this behavior on other nations.
Today the idea of just war persists in two related forms. Firstly, there is the historical moral tradition reaching back through “the laws and customs of war” to Aquinas, Gratian and his canonist successors, and beyond. Secondly, there is the developing body first called the laws of war, then the laws of armed conflict, and today, with the systematic incorporation of human rights law, international humanitarian law.
Two elements are central in both just war thinking and in international law relating to armed conflict: the requirement that noncombatants not be directly and intentionally attacked by parties engaged in armed conflict and the requirement that such parties fight so as to avoid producing disproportionate destruction. These two requirements are shared by both moral thought on just war and international law seeking to regulate the practice of war. In US military circles a third requirement is frequently added to these: that any act during war be militarily necessary. This language is also found in the law, but moralists generally regard military necessity as implicit in the other two requirements and particularly that of noncombatant immunity.
So far as concerns resort to war, the just war requirements of sovereign authority, just cause, and right intention have, for practical purposes in the conduct of international affairs, been superseded by the provisions of the United Nations Charter. Article 2 of the charter defines cross-border uses of military force by one state into the territory of another as aggression and therefore illegal. The broader provisions of Article 51 place the right to use force, apart from self-defense, as belonging exclusively to the Security Council and not individual states. Nonetheless, both the moral concerns embodied in just war tradition and the legal concerns in international humanitarian law have been used to argue for the use of military force in cases of humanitarian intervention, even without formal approval by the Security Council.
The focus of serving military personnel, though, properly should be on the parameters set on war-fighting by the moral tradition and international law. This returns us to the provisions on noncombatant immunity and proportionality.
In small wars these provisions are difficult to honor for various reasons. There is typically no third-party oversight of such conflicts to provide an independent perspective on how the conflict is fought. In civil wars and insurgencies it is common for both adversaries to define all supporters of the enemy side as combatants so that they may be attacked directly and intentionally. In cases of ideologically inflamed conflicts or religiously rooted terrorism this same feature is especially problematic, as those with different beliefs can easily be defined as inherently combatants. Finally, in any armed conflict involving relatively small forces, often constituted by ad hoc means, there is typically insufficient centralized oversight and, as a corollary, channels of responsibility and accountability often break down. When something goes wrong—as when noncombatants are directly attacked—who is responsible? In the context of small wars and insurgencies this is often disputed.
What this tends to mean for forces from the militaries of well-constituted and well-regulated states is that they must follow the rules, whatever they observe their adversaries to do. In the armed conflict between US forces and ISIS in Syria, for example, this meant that ISIS combatants could (and did) directly attack noncombatants for their own reasons but the US forces could not attack ISIS noncombatants in retaliation. In such armed conflicts following the rules—moral, legal, or both—becomes a one-sided affair, but nonetheless the rules must be observed.
This is a particularly problematic feature of small wars in which the forces of major powers become involved, but it may extend to larger wars involving the forces involved on both sides. The conduct of Russian forces in the war in Ukraine provides a striking example of this. These forces have repeatedly and systematically laid waste to houses and apartments, schools, libraries, and indeed any and all forms of the infrastructure associated with civilian—that is to say, noncombatant—life. Moreover, repeated evidence has emerged of direct, intended targeting of Ukrainian civilians in areas where Russian forces have been in control or even only passed through.
The status of all this behavior in relation to international law may or may not eventually be adjudicated in war crimes trials, but in any case this behavior by Russian forces is strikingly at odds with the just war norms of noncombatant immunity and proportionality of means. For practical purposes, just war norms seem to have no effect on the war-fighting behavior of the Russian forces in Ukraine. The behavior of the Ukrainian forces, by contrast, stands up well by both the moral standards of just war and international legal standards.
The Russian Federation has, of course, agreed to be bound by the rules for war-fighting set in international law, whatever the actual behavior of the Russian forces has been. It is perhaps worth noting that Russian military forces have a considerable history of indiscriminate and disproportionate behavior reaching back into history as far as the Napoleonic wars. In the present conflict there is, at minimum, a broad gap between what the Russian state has agreed to and how the Russian forces behave in war. This gap can, in principle, be closed, though given the historical record it seems unlikely.
The case is even more unpromising in relation to the moral norms of just war. While just war tradition came together and developed in Western European history as a broad cultural consensus spanning both religious and temporal life and institutions, Russia’s historical development took place outside this consensus and the period of Communist government only reinforced this separateness. Russian moral and political thinking has never adopted the just war idea and there is no sign of its presence there today. The war in Ukraine reflects this reality.
Turning to the case of China, there are many cultural differences between China and the West that are deeper and more striking. However, China has its own tradition—or rather, body of traditions—comparable to the Western tradition of just war, with contributions from across the whole spectrum of the major Chinese philosophical schools. Two Chinese terms translate as “just war”: yizhan, which appears in the classic literature and also carries the meaning of “righteous war,” and the present-day term zhengyi zhanzheng. Historically and politically the Chinese traditions of just war originated in the context of internal warfare in China and had as a major element the unification of China under a righteous government and defense against both internal and external threats. They reach back through several of the major periods of Chinese history as far as the 8th century BCE; thus collectively they are far older than Western just war tradition in its classic form. Yet prominent themes in the Chinese traditions parallel themes found in Western just war tradition, including avoidance of war when possible, awareness of the evil and tragic results of even just wars, respect for the well-being of the civilian population, the condemnation of aggressive war, and the importance of defense as a justifying cause for using arms.
Mao Zedong, using both the classical and contemporary terms for just war, defined just war as that made by oppressed people against their oppressors and unjust war as that made by oppressors. Contemporary Chinese doctrine reflects this conception, understood to mean that for China just war is always defensive and in support of justice. Mao did not write on the war-fighting limits in the Chinese just war traditions. Yet they remain, and the question is whether and how they are understood as binding for contemporary warfare.
Both the writings of Mao and the Seven Military Classics are read as elements of the military education of officers in the People’s Liberation Army. They are also reflected in Chinese military doctrine, which focuses on homeland defense. However, the broader Chinese strategic framework defines homeland defense in terms of overlapping circles reaching out into much of the western Pacific. This, coupled with Mao’s definition of defense as reaction to oppression, means that much US military activity in this region is seen by China as threatening. What it might take to be read by China as an aggression deserving a military response is not clear.
In recent years China has restructured its military organization at the strategic level as well as built up elements of its military forces, particularly the PLA Navy and the PLA Rocket Forces. The emphasis here has been coverage of the area included in the four strategically defined rings or circles. Andrew Scobell of the RAND Corporation defines these as follows. The first circle includes everything within the borders of the PRC. The second encompasses the near periphery, with its defining circle reaching from Korea south and east of Taiwan, then continuing down around the East and South China Seas, encompassing several Southeast Asian countries and ending with China’s regional rival India. The third ring includes China’s entire Asia-Pacific neighborhood, reaching beyond Hawaii to the east, Japan to the north, and Australia-New Zealand in the south. The fourth ring includes the remainder of the world. The key areas are those inside the first and second strategic rings. While there are civilian population centers in potentially hostile territories in this area, China has no history of behavior like that of the Russian forces in Ukraine, directly attacking with intent to destroy such centers. Rather, taking Taiwan as a significant example, the PLA Naval and Rocket Forces capabilities fit a Chinese strategic aim of preventing close support by US carrier groups in event of an armed conflict over Taiwan. China regards Taiwan as part of China; so extending Chinese rule over Taiwan would fit the historical Chinese just war categories of unification and establishment of just/righteous rule. But by the same measure destruction of Taiwanese civilian lives and infrastructure is precluded. This suggests that in a possible military conflict between the US and China the avoidance of direct and intended harm to noncombatants, a goal of both Western just war thinking and of Chinese just war traditions, could be honored.
In the end, then, the relevance of just war thinking depends in no small part on the nature of the adversary and the conflict. In small wars, insurgencies, and conflicts based in terrorism, all the concerns identified earlier suggest that the effort to honor just war ideals will likely be one-sided. In an armed conflict with Russia this may also be the case because of the lack of an indigenous respect for these ideals in Russian culture and historical political and military behavior. The case may be different, though, in a potential military conflict between United States forces and those of China. China has an ancient and well founded body of moral and political traditions on just war whose contents significantly parallel those of Western just war tradition. Also, for reasons having to do with the specific likely geography of such a conflict, both the Chinese and the Western just war traditions would be in immediate play.
All the types of conflict discussed above would impose substantial challenges to core elements of just war thinking. They would be different in each type of conflict, but the outcomes need not be solely negative.