Just War and Likelihood of Success: Wars of Necessity vs. Wars of Choice

Abstract

This article makes an argument about the right place of the likelihood of success principle in just war thinking. Its analysis is grounded in a neoclassical reading of just war that is applied to the ongoing Russian war of aggression against Ukraine. The article starts with an exploration of the status of the likelihood of success principle in contemporary just war thinking. Noting that the difficulty of applying this principle has been pointed out by various thinkers, the chapter adapts the distinction between the so-called deontological and prudential just war principles found in neoclassical just war thinking. This distinction holds that the deontological principles hold primary importance within the logic of just war, and the prudential principles, including likelihood of success, are of secondary importance only. The article continues with an assessment of the practical implications of this distinction by applying it to two different types of warfare, namely so-called “wars of necessity” and “wars of choice.”

Keywords:

• just war
• likelihood of success
• wars of necessity
• wars of choice
• ethics in war

In the immediate aftermath of the full-scale Russian invasion of Ukraine in February 2022, the then-Ukrainian ambassador to Germany, Andrij Melnyk, had a meeting with Christian Lindner, Germany’s finance minister. According to Melnyk, Lindner told him, “You have a few hours,” and it would make no sense to supply Ukraine with weapons or to exclude Russia from SWIFT (The Odessa Journal 2022). Rather, Germany and the West should be prepared to deal with the inevitable defeat of Ukraine, including doing business with a possible Russian puppet regime in Kyiv. In making that gloomy prediction, Lindner was far from alone. Reportedly, three U.S. officials, speaking anonymously, told Newsweek that Kyiv would fall within a few days and Ukraine’s resistance would be put down shortly thereafter (Jamali, Brennan, and O’Connor 2022). In other words, there were influential voices in the West that had serious doubts about Ukraine’s likelihood of success in its war of self-defense against Russia. To them, it seemed, Ukraine had to reconcile itself with the ancient truth that the Athenian historian Thucydides had captured so succinctly many centuries ago: “The strong do what they can and the weak suffer what they must.”

Thucydides’s famous saying, commonly seen as capturing the gist of the school of realism, puts a premium on hard power and does not seem to include ethical considerations. Interestingly, the just war tradition, the oldest tradition of Western ethical thinking about the rights and wrongs of war, also includes a principle that could be interpreted in a way that allows for Lindner’s calculus, namely, the likelihood of success principle. While warning against too narrow an interpretation of the principle, Charles Guthrie and Michael Quinlan (2007, 31) characterize the principle as emphasizing that,

it cannot be right for a national leader, responsible for the good of all the people, to undertake—or prolong—armed conflict, with all the loss of life and other harm that entails, if there is no reasonable likelihood that this would achieve a better outcome for the people than would result from rejecting or ending combat and simply doing whatever is possible by other means.

Consequently, if one were to follow a strict interpretation of just war that all its principles must be fully met for a war to be morally justifiable, the assessment that Kyiv will fall within days would make Ukraine’s war of self-defense unjustifiable. Noting that this paper is being written in the third year of the war against Ukraine, it of course benefits from knowing what happened in the two years after the Melnyk-Lindner meeting. While it is impossible to predict the future of the ongoing war, Ukraine has forcefully contradicted the early pessimistic predictions cited above and managed to fight Russia to a stalemate in its eastern regions. In this regard, it is noteworthy that the courageous Ukrainian war effort has, to a significant extent, been enabled by Lindner’s government, which, after initial hesitation, has become Ukraine’s main European supplier of arms. Consequently, there is reason to investigate the intellectual merits of the likelihood of success principle in just war, whose purchase Ukraine seems to have diminished, noting that the country’s war against Russia has turned into a modern paradigm case for a “just war.” How should the principle be understood vis-à-vis contemporary warfare? What is its role in relation to the other just war principles? Is it perhaps even obsolete, given the powerful case of Ukraine that could be held against it?

In terms of outline, this article starts with an exploration of the status of the likelihood of success principle in contemporary just war thinking. Noting that the difficulty of applying this principle has been pointed out by various thinkers, the chapter adapts the distinction between the so-called deontological and prudential just war principles found in neoclassical just war thinking. This distinction holds that the deontological principles hold primary importance within the logic of just war, and the prudential principles, including likelihood of success, are of secondary importance only. The article will go on to grapple with the practical implications of this distinction by applying it to two different types of warfare, namely so-called “wars of necessity” and “wars of choice.” Grounded in an engagement with the concept of the common good, the article concludes that in wars of necessity, such as Ukraine’s war of survival against Russia, the moral purchase of the likelihood of success principle is diminished. Regarding wars of choice, however, such as the 2003 Iraq War, it continues to be an important prudential consideration that political decision-makers need to carefully consider when making their jus ad bellum judgments.

Likelihood of Success in Contemporary Just War

Looking at contemporary just war thinking, it seems fair to argue that the likelihood of success principle is among the most difficult to apply in practice. On the one hand, Guthrie and Quinlan (2007, 32), following their definition provided above, suggest that any fighting in the absence of a likelihood of success needs to be weighed against the common good of the people the war aims to protect:

It is sometimes suggested that, even in hopeless causes, armed resistance can be legitimate as an upholding of national or moral values. This perhaps cannot be ruled out totally, but it would need to be assessed warily and indeed skeptically, since in practice it could too easily shade into defending the pride or obstinacy of the ruler rather than the interests of the people.

On the other hand, however, Brian Orend (2013) highlights the challenges that the weaker side in a war inevitably faces. “Great care,” he argues, needs to be taken to avoid “rewarding aggression” when the weaker side in a war assesses the likelihood of success principle (Orend 2013, 61). In addition, Orend makes the important observation that history teaches us that it can be hard to judge the likelihood of success in practical terms, and there are many accounts of the weaker side prevailing in conflicts that have become “the stuff of military legend” (61). Of course, in the end, only history will be able to tell, but arguably the first two years of Ukraine’s war of self-defense against Russia come close to deserving a place in the category of military legend, as against the gloomiest of predictions Kyiv has not fallen, and Ukraine even managed to launch a counteroffensive in 2023.

As students of just war know, historically the tradition has benefited from numerous influences, including philosophy, law, lessons learned from statecraft and military affairs, as well as theology. The two sources cited in the previous paragraph represent three of these influences. Field Marshal the Lord Guthrie is a senior military leader, the late Sir Michael Quinlan was a senior UK civil servant, and Brian Orend is one of the leading contemporary philosophers working on the ethics of war. Considering the readership of this journal, it is thus of interest to also consider the theological perspective on the likelihood of success principle. There is, of course, a multiplicity of theological voices, but a turn to the Catholic position will prove especially insightful. Indeed, the Catholic Church can legitimately claim to be the most enduring and influential theological contributor to the conversation about the rights and wrongs of war.¹ The Catechism of the Catholic Church (1993, no. 2309) defines the principles governing what it calls “legitimate defense by military force” as follows:

The strict conditions for legitimate defense by military force require rigorous consideration. The gravity of such a decision makes it subject to rigorous conditions of moral legitimacy. At one and the same time:

• The damage inflicted by the aggressor on the nation or community of nations must be lasting, grave, and certain;

• All other means of putting an end to it must have been shown to be impractical or ineffective;

• There must be serious prospects of success;

• The use of arms must not produce evils and disorders graver than the evil to be eliminated. The power of modem means of destruction weighs very heavily in evaluating this condition.

These are the traditional elements enumerated in what is called the “just war” doctrine. The evaluation of these conditions for moral legitimacy belongs to the prudential judgment of those who have responsibility for the common good.

As a result, the likelihood of success principle also plays a role in the Catholic conversation about the justifiability of armed force. In fact, the Catechism highlights a crucial point to which I will return later, namely, the argument that the application of the just war principles should be seen as a prudential judgment by those responsible for the common good.

Deontological and Prudential Just War Principles

So, how can we make sense of a principle that seems notoriously challenging to apply? As is often the case, an engagement with history can provide answers. While much of contemporary just war thinking has been taking place before the horizon of what I have called “the fight for the just war tradition” (Braun 2023), a historical, or neoclassical, approach to just war can provide important insights into the question of how to deal with likelihood of success. In my own work, I tend to go back to the work of St. Thomas Aquinas (1224/5-1274,) who systematized the classical just war by bringing together the multiple influences I have listed above. Aquinas’s succinct summary of what constituted a just war had and continues to have a profound influence on how we think about the ethics of war and peace today. Importantly, in his (1948, II-II, a. 40, q. 1) seminal definition of just war, Aquinas listed only three jus ad bellum principles (legitimate authority, just cause, and right intention). The remaining three principles of contemporary just war (proportionality, likelihood of success, and last resort) are not found in Aquinas. At least, that is, Aquinas did not imagine those considerations as distinct principles. That should not be interpreted as them being of minor importance only, but arguably, these considerations had a place in Aquinas’s understanding of right intention, which asks those in authority to aim for a just peace.

Drawing on the classical idea of just war, James Turner Johnson, the pre-eminent historical just war thinker, provides an important distinction that can inform the response to the question about the likelihood of success principle raised above. Building on the thought of thinkers like Aquinas, who proposed three jus ad bellum principles only, Johnson (1999) makes a distinction between what he calls deontological and prudential just war principles.

For Johnson, the deontological principles of legitimate authority, just cause, and right intention are of primary importance, whereas the prudential principles of proportionality, likelihood of success, and last resort are secondary only in the logic of just war analysis.² Not at all does he seek to suggest that the prudential just war criteria are of minor importance, but they are trumped by the deontological criteria. As Johnson (1993, 43) puts it succinctly:

It is one thing to argue that a particular use of force (…) meets the requirements of just cause, competent authority, and right intention but cannot reasonably be expected to succeed and may cause more harm than good; this is how the jus ad bellum criteria should properly be brought to bear on a given decision. It is quite another thing to argue that lack of reasonable hope of success or proportion of good over harm (…) removes all moral justification for use of force; this is a misuse of the jus ad bellum criteria.

In other words, Johnson makes the important observation that while a war that struggles to fully meet the prudential jus ad bellum principles is relatively less justifiable than a war that meets all of them satisfactorily, that should not be taken to deny the overall justifiability of the war, depending on the specific circumstances. Returning to the Catholic just war that in its modern manifestation has been emphasizing the theme of restraint over that of permission, Johnson (2016) has taken a very critical stance, a significant reason for which has been the emphasis of the prudential just war criteria, including likelihood of success, by major voices within the Church. In Johnson’s (2016) eyes, the contemporary Catholic “presumption against war” starts from the position that any use of armed force should be seen as unjustifiable unless all of the jus ad bellum criteria have been met and the presumption can thus be overruled. In such assessments, the prudential criteria receive considerable attention, which results in a very restrictive attitude towards armed force. For Johnson, this is what he calls “a form of crypto-pacifism” (2016, 45–46).³

To my mind, Johnson’s interpretation provides important lessons for how to deal with the likelihood of success principle in contemporary warfare. In fact, his distinction between the deontological and prudential just war criteria goes beyond the likelihood of success principle and applies to proportionality and last resort, too. If one does not seek to escape to far-fetched, sterile thought experiments and prefers to grapple with real-world cases of armed conflict, I doubt that it will be possible to find any war where the interpretation of jus ad bellum principles is beyond questioning. Those “in authority” are facing an unenviable task in figuring out how the jus ad bellum principles apply to particular cases. However, they bear responsibility for the common good of the people entrusted to them and that responsibility requires them to make tough decisions. In that light, even if some of the prudential principles do not seem to be met completely, there may be cases where going to war is justifiable.

The notorious uncertainty of war may also require politically prudent reassessments of a country’s war effort. Again, the war against Ukraine is a testament to this. Reportedly, early into the war, President Zelensky had signalled some flexibility regarding the status of Crimea. However, after it became clear that Ukraine’s war effort was beating many expectations, Zelensky adopted a maximalist position that insisted on a complete Russian withdrawal from all of Ukraine, including Crimea (Vohra 2023). In other words, Zelensky redefined what success would mean for Ukraine based on what in German is known as Kriegsglück, the fortunes of war. My contention is that it falls to those “in authority” to define what success means, and there may be circumstances where a questionable likelihood of success should not be taken to deny the overall justifiability of a war. That does not mean that such a war would be perfectly “just” (I personally struggle with the clarity of the term “just” anyways), but it might be justifiable. In what follows, I will engage with this matter grounded in the distinction between wars of necessity and wars of choice. I will argue that there are reasons not to overstate the significance of likelihood of success in the former category. At the same time, I hold that the prudential test of likelihood of success should be seen as an important obstacle against going to war in cases where the common good of the own political community is not at risk.

Likelihood of Success: Wars of Necessity vs. Wars of Choice and the Common Good

Writing after the experience of two U.S. wars against Iraq, one in 1991, the other in 2003 and thereafter, Richard N. Haass (2009) introduced an important terminology that can help to make moral sense of the likelihood of success principle of just war. According to Haass (2009, xvii),

Wars of necessity involve vital interests and the inability to protect them by means other than military force. The first Iraq war, triggered by Saddam Hussein’s August 1990 invasion and occupation of Kuwait, was a war of necessity. The interests at stake—preventing hostile domination of the lion’s share of the world’s oil, setting a constructive precedent for the era of international relations just dawning in the wake of the Cold War—were truly vital, and neither diplomacy nor sanctions (both of which were tried) nor anything else other than resorting to force could safeguard them.

Wars of choice, however, seem to differ markedly in the reasons for why they may be undertaken:

Wars of choice are just that, and involve uses of military force either on behalf of lesser interests (in which case, there is the option of not acting) or when alternative policies are available (in which case, military force may not be the preferred approach). The second Iraq war, initiated by George W. Bush in March 2003, was a war of choice. There was no pressing threat to U.S. interests, and there were any number of policy alternatives available, with shoring up existing sanctions against Iraq among them. (Haass 2009, xviii)

Consequently, what distinguishes the two types of war is the question of how fundamentally important are the interests that are at stake. Grounded in the experience of the 2003 Iraq war and the war in Afghanistan, as well as the 2011 intervention in Libya, the distinction between wars of necessity and wars of choice became an important factor in policy debates, not just in the U.S., but in most NATO countries, too. It seemed that after the costly wars of choice listed above, especially Iraq, the appetite to engage in wars where vital interests were not immediately at stake had reduced dramatically. Consider, for example, President Barack Obama’s September 2013 speech to the nation in which he laid out his rationale for intended limited airstrikes against Syria’s Assad regime in response to its use of chemical weapons against the civilian population. In this speech, Obama (2013) emphasized that he had previously “resisted calls for military action, because we cannot resolve someone else’s civil war through force, particularly after a decade of war in Iraq and Afghanistan.” In other words, Obama was not interested in fighting another war of choice.

I hope the reader does not mind the personal anecdote that at both the Royal Military Academy Sandhurst and the UK Defence Academy, where I have lectured, the distinction between wars of necessity and wars of choice continues to be an important one. In fact, the distinction has only increased in significance in the aftermath of the Russian war of aggression against Ukraine, with which I started my argument. It will come as no surprise to the reader that current defense debates in NATO revolve around the question of how to best prepare militaries for scenarios of future major combat operations against peer competitors such as Russia and China. Put differently, to prepare for wars of necessity again after two decades of fighting wars of choice in foreign lands, wars that were oftentimes counterinsurgency campaigns where no vital national interests were at stake. Importantly, as I will argue in the following section, the distinction between wars of necessity and wars of choice, to my mind, provides the answer to the question about the rightful place of the likelihood of success principle.

Drawing on a distinction between two common goods, a national and a universal one, that corresponds to the wars of necessity vs. wars of choice dichotomy, I will argue that it can be the right thing to do morally speaking to engage in both wars of necessity and wars of choice, but the prudential considerations those in authority need to take into account are not of the same importance as the deontological principles. I hold that the reason for this is that while there is a moral responsibility to care for both the national and universal common good, primary care is due to the national common good. Consequently, in wars of self-defense, such as Ukraine’s war of survival against Russian aggression, the role of the likelihood of success principle, to use Johnson’s phrasing, is indeed secondary.

The Two Forms of the Common Good

As will become apparent shortly, the common good is a concept that is not alien to just war. Rather, for the classical just war and today’s neoclassical thinkers who seek to learn from it, the common good has always been at the very heart of thinking about when going to war can be morally justifiable. Before turning to the content of the concept itself, it is worth pointing out that while the Western understanding of the common good has mainly been shaped by Christians, the concept was already present in pre-Christian times. Interestingly, on this aspect, the common good parallels just war thinking, which also significantly precedes Christianity, depending on where one wants to situate the historical starting point. In addition, it is of interest to note that while the content of the concept has been shaped by Christianity, in another parallel with just war, the concept of the common good, in the distinction between its national and international forms, has entered the secular debate, including the realist school of International Relations. The concept of the common good has been an important concept in moral and political philosophy both for pre-modern and modern thinkers. However, while both pre-modern and modern thinkers have argued about the common good, a shift in their respective understanding of the concept can be detected. While pre-modern thinkers imagined the common good as part of an ideal community that could only be realized by a life of virtue, modern thinkers like John Rawls (1921-2002) have foregrounded the political conditions that are needed for individuals to obtain personal ends (Jade 2017).

The historical origin of thinking about the common good can be traced back to Greek and Roman sources, especially the work of Aristotle (384BCE-322BCE) and Cicero (106BCE-43BCE). For the purpose of this article, I turn to the thought of Aquinas. Just like he did for his discussion of just war, Aquinas drew on the work of his predecessors to argue about the common good, including Aristotle and Cicero. Importantly, that is not to say that Aquinas was the first Christian thinker to write about the common good, as Augustine of Hippo (354-430) had already discussed questions related to the ethics of war and peace in the context of the common good (Johnson 2016). It should also be noted that, in contrast to his treatment of war, Aquinas did not dedicate a specific question to the common good. However, after his death, Aquinas’s Summa Theologiae took on a seminal status for the thinking of the Catholic Church, an influence that continues to inspire contemporary Catholic natural law thinking, including thinking on the common good and how it relates to international politics (Hollenbach 2002).

Aquinas (1948, I-II, q. 90, a. 2) imagines the common good in reference to particular goods:

Actions are indeed concerned with particular matters: but those particular matters are referable to the common good, not as to a common genus or species, but as to a common final cause, according as the common good is said to be the common end.

In his article on justice, Aquinas (1948, II-II, q. 58, a. 5) explains further how one part contributes to the whole:

Now it is evident that all who are included in a community, stand in relation to that community as parts to a whole; while a part, as such, belongs to a whole, so that whatever is the good of a part can be directed to the good of the whole.

Naturally, the common good also needed to be protected against outside attack. Aquinas justified the use of armed force in the name of the flourishing of the respublica and the common good (Reichberg 2017). The importance Aquinas allocated to the common good in his thinking about war and peace was also one of the reasons why he discussed war within his treatment of charity, the highest of the so-called theological virtues (2017).

Crucially, the concept of the common good also speaks to the question of how to conduct affairs among political communities. For Aquinas, the common good would be more than the flourishing of individual political communities. Rather, Aquinas identified a universal moral order to which all human beings belonged. Following from that, coming with the challenge of avoiding an anachronistic reading of Aquinas, one might argue that similar to the relationship between the individual and the political community in the domestic context, individual political communities are situated within a community of communities that share a higher common good. Arguing this way, one should emphasize that such a reading relies on an interpretation that has not been embraced unanimously.

Bruno de Solages (1895-1983), for one, was of the opinion that when arguing about just war, Aquinas had in mind only the domestic common good of the political community that had been entrusted to a particular prince. An international common good, according to De Solages (1946), was not on Aquinas’s mind when he wrote his article on war in the Summa Theologiae. Without a doubt, Aquinas did not have an understanding of international affairs that reflected the contemporary idea of an “international community.” Gregory Reichberg, however, thinks that de Solages is “somewhat too emphatic” in his rejection of an international common good as a factor in Aquinas’s bellum justum (2017, 135–136, fn. 98). Noting that the term was clearly only introduced long after Aquinas, Reichberg identifies indicators that a distinction between a domestic and an international common good vis-à-vis the ethics of war was not a thought that would have been alien to Aquinas. The most obvious reason for this is Aquinas’s argument that waging an unjust war disrupted the friendship of one polity with another. Because friendships rely on a shared good, a common good like this is considered to rest above the domestic common goods of the respective polities.

Lending further credit to this specific interpretation of Aquinas is that it is well established that the classical understanding of just war imagined a moral responsibility of princes “for the common good of their own political communities and, both individually and collectively, for maintaining the structure of relations among such communities that allows each to enjoy its own good” (Johnson 2016, 17–18). In that sense, unjust wars against third parties, although not an attack on oneself, were an attack on the structure of relations among communities that endangered the own common good or could do so at some point in the future. Following from that, the structure of relations was worth protecting. It marked an international common good, at least of a sort.

That said, the “internationalization” of the common good is widely considered to be a twentieth-century development. J. Bryan Hehir (2007, 17), for one, argues that the “expansion of the common good beyond national boundaries” first happened in the 1960s when Pope John XXIII spoke of the “universal common good”:

Today the universal common good presents us with problems which are world-wide in their dimensions; problems, therefore, which cannot be solved except by a public authority with power, organization and means co-extensive with these problems, and with a world-wide sphere of activity. Consequently the moral order itself demands the establishment of some such general form of public authority. (Pope John XXIII 1963)

Ever since, the distinction between a national and a universal common good has been a prominent theme in the Catholic argument about global justice (National Conference of Catholic Bishops 1983; 1993).

So What? The Common Good and Likelihood of Success

Commonly, the distinction between the domestic and the universal or global common good is invoked to argue for a responsibility of the developed nations to support the development of the less well-off. Arguments such as “with power and influence comes a responsibility to contribute to the universal common good” are frequently put forward to remind the rich and powerful not to forget about the responsibility for all humankind (National Conference of Catholic Bishops 1993). Interestingly, with most attention going to the question of what is morally required to advance the global common good, the question of how to respond when the two conflict has not been at the center of attention hitherto. However, it also has important lessons for the wars of necessity vs. wars of choice dichotomy and how it applies to the likelihood of success principle. Having noted the importance of the common good for acting ethically in international politics, what can we learn from it regarding the likelihood of success principle?

Writing about “the morality of national interest,” a term commonly associated with realism, Nigel Biggar (2013, 231–232) has pointed to the Thomistic understanding as making an illuminating contribution. Noting that Aquinas combined “the Book of Genesis’s affirmation of the goodness of creation with Aristotle,” Biggar (2013) argues that Aquinas does not reject all self-interest as morally indefensible. Rather, according to Biggar, Aquinas “holds that there is such a thing as morally obligatory self-love.” In the same way that an individual has a moral duty to care for herself, national communities and the governments who represent them are duty-bound to care for the well-being of their own people, or, to use a different term, the national interest. Biggar goes on to argue that a nation’s pursuit of its national interest must not ignore the rights of others. However, acting in national self-interest does not need to result in acts of injustice at the cost of others.

To my mind, Biggar’s interpretation of Aquinas provides important insights for developing an understanding of the rightful place of the likelihood of success principle in just war analysis and the other prudential principles more generally. Arguably, there is a moral obligation to advance the universal common good, which certainly includes the likes of fighting poverty and climate change but which also may include, depending on the circumstances, military action beyond immediate self-defense. That said, circumstances do matter, and prudential considerations may advise against taking military action, although such action might well meet the deontological just war criteria. To provide a practical example, Haass’ example of a war of choice, the initiation of the 2003 Iraq war, received the approval of thinkers like Johnson (2005) and Biggar (2013), who emphasized the importance of the deontological just war criteria in their analyses. At the same time, as many readers will recall, there were critics who argued that removing Saddam Hussein would not create the “beacon of democracy” in the Middle East that some interventionists were seeking to establish. These critics did in no way justify the brutal rule of the dictator in Baghdad, but they were worried that toppling an illegitimate ruler might cause unforeseeable negative consequences in Iraq and the Middle East more broadly.

Acknowledging that there is some flavor of retrospective reasoning to this argument, the post-war chaos that eventually led to the rise of the so-called Islamic State and another Western military campaign that is still ongoing as I write arguably highlights the importance of the likelihood of success principle for wars of choice.⁴ In other words, when the national common good is not directly threatened, those in authority are asked to weigh the prudential just war principles, especially likelihood of success, carefully when considering the use of armed force in wars of choice aimed at the universal common good.

The case for wars of necessity, however, is different. Putting down one’s arms in a war that meets the deontological just war principles simply because the unjust attacker is stronger militarily seems irreconcilable with the responsibility those in authority hold for the common good of their political community. Put differently, in wars of necessity, such as Ukraine’s war of survival against Russian aggression, the likelihood of success principle should not be taken to delegitimize the war effort of the weaker side. Otherwise, Orend’s warning against “rewarding aggression” that seems inherent to uplifting the likelihood of success principle to quasi-deontological status will be ignored. The classical just war took that warning very seriously; arguably, contemporary interpretations that start from a presumption against war would benefit from remembering this insight. One of the reasons why Aquinas did not spell out any distinct prudential just war principles was the emphasis he gave to the principle of right intention, which put a premium on good statecraft undertaken by those in authority. In that sense, Johnson is correct that the prudential principles of just war, although not unimportant, are of secondary relevance vis-à-vis the deontological principles.

Thus, returning to the heroic war effort of Ukraine once more, fighting nominally superior Russian armed forces, and more generally, a state that is demographically and economically stronger, does not make this war of necessity unjustifiable. It is part of President Zelensky’s job description to apply the prudential just war principles, including likelihood of success, prudently. Giving in to Russian aggression, to borrow Biggar’s expression, would deny the “morally obligatory self-love” the just war tradition asks legitimate authorities to demonstrate.

Conclusion

Returning to the meeting between the Ukrainian ambassador and the German finance minister, it is important to note that Germany has gone through a remarkable development in the two years after the full-scale Russian invasion of Ukraine. The initial hesitation to support Ukraine with lethal weapons has made way for Germany’s role as Europe’s main supporter of Ukraine. Arguably, Germany has switched from a realist position that could be detected in Lindner’s remarks to one that considers its responsibility for both the national and universal common good. Besides supporting Ukraine in its “just war” against Russia, it seems that Germany has come to realize that its post-Cold War tendency of seeking to cash in the peace dividend has reached its limits in the light of Russian aggression. Put differently, the war against Ukraine has turned into a war of necessity for Germany in the sense that seeing Ukraine succeed is now considered a core national interest, whereas Lindner’s previous rhetoric seemed to contradict that assumption. Ukraine, of course, was forced to come to that realization much earlier.

What is at stake for Ukraine is its very survival as an independent nation. Having that in mind, I have argued in this article that the just war tradition and related thinking about the common good requires that the so-called prudential principles of just war, including the likelihood of success principle, are applied differently in wars of necessity and wars of choice. This should not be taken to mean that the prudential principles are unimportant, but a reduced likelihood of success should not be taken to deny the overall justifiability of a war of necessity. In wars of choice, more weight should be given to prudential considerations. In the end, however, the just war tradition teaches us that it is only those who hold responsibility for the common good who are entitled to take those decisions.

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Christian Nikolaus Braun

Christian Nikolaus Braun is a lecturer in the Defence Studies Department at King's College London. His primary area of research is the ethics of war and peace. Christian’s work has been published in numerous academic journals, including Ethics & International Affairs, International Relations, International Theory, and the Journal of Military Ethics. He is also the author of Limited Force and the Fight for the Just War Tradition (Georgetown University Press).

Notes

1 For two recent assessments of the state of affairs in contemporary Catholic thinking on the ethics of war, see Braun (2020a); Reichberg (2017, chap. 11).

2 Johnson distinguishes between seven jus ad bellum principles, listing also the aim of peace. I prefer to use the more common framework of six principles, subsuming the aim of peace within the right intention principle.

3 For a detailed discussion of Johnson’s assessment of the Catholic Church’s just war teaching, see Braun (2020b).

4 See Braun (2023, 112–115) for a more detailed discussion of the 2003 Iraq war and the arguments made by neoclassical just war thinkers at the time.