Weapons for Ukraine as force-short-of-war

Abstract

This article presents arguments about the ethics of sending weapons to Ukraine in support of its war of self-defence against Russian aggression. It does so by situating the debate about the rights and wrongs of supplying arms to Ukraine within the frame of jus ad vim (the just use of force-short-of-war). Concentrating on the German debate, which has been particularly polarized, the article demonstrates how the moral vocabulary of jus ad vim can illuminate the difficult moral choices associated with providing lethal aid to Ukraine. In particular, the article shows how the objective of not getting drawn into war with Russia foregrounds the ‘probability of escalation’ principle of jus ad vim. In addition, the German chancellor's avoidance of the term ‘victory’ as the desired outcome of his nation's support for Ukraine points to the concept of a ‘moral truncated victory’ and the re-establishment and containment principles of jus ad vim. However, while the moral vocabulary of jus ad vim leads to a deeper understanding of the ethical challenges NATO leaders are facing in their provision of weapons to Ukraine, the article concludes that the acceptance of moral truncated victory highlights one of the main critiques of this new framework, namely that it risks creating a morally problematic regime of perpetual force, or vis perpetua.

Russia's war against Ukraine, following the full-scale invasion of 24 February 2022, marks the largest armed conflict on European soil since the Second World War. The shock the war has caused within the international community has been profound, precisely because large-scale war had widely been seen as a relic of days past. Instead, limited force was considered to be the dominant face of contemporary armed conflict. After the end of the Cold War, the West had no longer been facing the threat of a peer-on-peer war; it became engaged in an asymmetrical ‘war on terror’ and so-called wars of choice that were markedly different to the currently ongoing war against Ukraine. NATO, while eager to help Ukraine to defend itself against an unjust attack, has been outspoken about not intending to become a party to the war. One—if not the most important—reason for seeking to avoid a direct involvement has been the threat of escalation, especially an escalation to nuclear war, and avoiding that scenario has underpinned the decision-making of Ukraine's main supporters. As a result, the supply of lethal support to Ukraine is grounded in an ostensible contradiction: the delivery of weapons, which may be designated as ‘force-short-of-war’, seems to be contingent on avoiding the most indiscriminate form of war: nuclear war.

In contemporary just war scholarship, thinking about alternatives to large-scale use of armed force has become a major field of interest. Under the umbrella of jus ad vim (the just use of force-short-of-war) just war thinkers have argued about the morality of force-short-of-war, or, to use the Latin word for force, vis.¹ The foundation for jus ad vim was laid by Michael Walzer almost two decades ago, when he grappled with the measures imposed on Saddam Hussein's Iraq after the Gulf War of 1991.² Reflecting on that sanctions regime, Walzer imagines those as ‘an experiment in responding differently’.³ Although some sanctions, such as the no-fly zone in northern Iraq, were acts of war in the legal sense, Walzer argues that they were markedly different compared to conventional warfare. To arrive at a deeper understanding of such action, he proposed a new framework of jus ad vim, situated between the ethics of war and the ethics of peace. Undergirding Walzer's thinking was the assumption that it is possible to demarcate the difference between war and force-short-of-war, which put him at odds with international law that considers both large-scale and more limited use of force as parts of armed conflict.

Within this emerging body of jus ad vim scholarship, a distinction can be made between broad and narrow accounts.⁴ The difference between the two is that the latter is exclusively concerned with limited use of kinetic force, whereas the former includes non-kinetic measures short of war, such as trade embargoes. To date, the narrow account has received most attention. For example, Daniel Brunstetter, in his pioneering monograph published in 2021, provides moral arguments about the imposition of no-fly zones, drone strikes, limited air strikes to enforce international norms, and special forces operations.⁵ However, while thinking about non-kinetic alternatives to war is on the rise, it has not yet been at the centre of attention, at least not in direct association with jus ad vim.⁶ This article seeks to address this lacuna by presenting arguments about the morality of delivering weapons to Ukraine. Indeed, supplying arms is a curious case for jus ad vim scholarship, as it seems to sit between the broad and narrow accounts. One might even question whether the jus ad vim category applies at all. After all, many of the weapons that have been sent to Ukraine, commonly characterized by their suppliers as ‘defensive’ weapons, have been used to unleash large-scale, not limited, force. That said, however, it is also true that the states who deliver weapons to Ukraine have made their decision dependent on not being drawn into the war between Russia and Ukraine. In other words, their support for Ukraine marks an act short of war in the sense that it lets them avoid a direct involvement in the war. Ukraine's supporters have provided Kyiv with the means to wage war as part of a policy that for them amounts to a use of force-short-of-war.

Concentrating on the broad account of jus ad vim, this article brings to bear just war thinking on the delivery of weapons to Ukraine. In the just war literature, while the morality of supplying arms has generally not been at the centre of attention, there is an emerging body of research on the morality of arming rebels.⁷ Providing arms to sovereign states, however, remains an under-studied area. Concentrating on the German debate, I argue that Germany's attempt to assist Ukraine, contingent on not being drawn into its war with Russia, highlights core insights of jus ad vim scholarship. I assert that avoiding an escalation of the war foregrounds the ethical considerations Brunstetter seeks to capture in the novel ‘probability of escalation’ principle he has proposed. When defining this principle, Brunstetter speaks of a

strong moral penchant against making the shift from the limited destruction of vim [sic] to the wide and unpredictable destruction of bellum … the probability of escalation principle serves to constrain jus ad vim by restricting recourse to limited force to circumstances where the decision to use limited force is very unlikely to lead to war.⁸

Thus, the moral vocabulary this principle provides differs from the established language of just war, and it is its focus on avoiding escalation to war that encapsulates the novelty and increasing relevance of thinking about jus ad vim.

Germany's stepwise increase of support for Ukraine, moving from non-lethal aid to advanced weapons systems, while at the same time still withholding particular systems and attaching restrictions on how the supplied systems may be used, seems to be undergirded by Chancellor Olaf Scholz's application of the probability of escalation principle. Directly following on from this principle, I show how taking the risk of escalation as the guiding star of German support for Ukraine implies accepting that Ukraine might at best be able to achieve a ‘moral truncated victory’, another crucial insight of jus ad vim scholarship regarding the limitations of force-short-of-war. As I will argue, the notion of a moral truncated victory is succinctly captured in Scholz's rhetoric that ‘Russia must not win and Ukraine must not lose’.⁹ This statement, as his critics charge, falls short of saying that Ukraine must win the war. In addition, arguably grounded in the notion of moral truncated victory, influential voices within Scholz's Social Democratic Party (SPD) have argued for ‘freezing’ the war, accepting that Russia's territorial gains in eastern Ukraine would be made quasi-permanent. The idea that a moral truncated victory is the best outcome that force-short-of-war is able to achieve leads the article to argue that supplying weapons to Ukraine amounts to a form of risk management. It unfolds in between the two extremes of Ukraine ceasing to exist as a sovereign state and an escalation of the war to a direct confrontation between NATO and Russia. Again drawing on insights of jus ad vim scholarship, the article concludes with an assessment of the ethical challenges that are inherent to adopting this strategy. It argues that supplying arms to Ukraine as a risk management strategy gives emphasis to one of the most powerful critiques that has been held against jus ad vim, namely, that it risks creating a state of vis perpetua, an endless state of force-short-of-war that would essentially reward Russian aggression.

Importantly, while achieving a moral truncated victory or creating a state of vis perpetua would be morally problematic, the use of force-short-of-war must be considered in comparison to the available alternatives. Arguably, both extremes—withholding any form of assistance or, legally speaking, directly participating in hostilities in support of Ukraine and risking a spread of the war across Europe—are even less morally justifiable. That is to say that although a just peace always functions as the horizon of just war thinking, such an outcome, more often than not, proves illusive. Not surprisingly, until Cian O'Driscoll's ground-breaking account, just war thinkers had relatively little to say about the concept of victory.¹⁰ Importantly, Brunstetter's account of jus ad vim, starting as it does from a presumption against war, acknowledges that the use of force-short-of-war may not be able to achieve the moral good a just war may bring, but it may be the least bad moral option available to state leaders at a particular moment in history. That is also one of the reasons why Brunstetter places thinking about jus post vim, the aftermath of using force-short-of-war, at the very beginning of his moral analysis.

The choice to concentrate on the German debate in this article is deliberate. I argue that Scholz's decision to take the risk of nuclear escalation as the determinant factor in his decisions about the quantity and quality of German arms deliveries, as well as in the rhetoric with which he justifies his actions, highlights the importance of grappling with force-short-of-war in unique ways. There are two main reasons for turning to the German debate. First, the German government's support for Ukraine has undergone a remarkable metamorphosis. Starting from a very hesitant position that was limited to non-lethal aid, Germany has increasingly stepped up its support and is second only to the US in terms of its supplies to Ukraine, which now include advanced weapons systems. This change of position seems to have been influenced by an altered estimate of Russia's reaction to such support. While the Russian threats of escalation felt more acute at the beginning of Germany's support, it appears that Scholz, in tandem with Germany's NATO allies, decided to expand arms supplies to Ukraine in the following months and years based on new assessments of the risk of escalation. At the same time, however, once more foregrounding the fear of escalation, Scholz continues to reject the supply of Taurus cruise missiles, does not allow Ukraine to use weapons supplied by Germany on Russian territory beyond the immediate vicinity of the Kharkiv region, and strictly opposes the suggestion of French President Emmanuel Macron not to rule out the deployment of NATO troops on Ukrainian soil. Second, due to the country's post-Second World War culture of military restraint, the German debate about supporting Ukraine, including the moral aspect, has been particularly heated. Although, unlike in the English-speaking world, the German debate rarely invokes the language of just war explicitly, both Scholz and his critics have justified their actions and arguments in moral terms, many of which directly speak to the ethics of force-short-of-war.

While this article focuses on the morality of war, the horizon before which it unfolds is also highly relevant to war's legal dimension. Unfortunately, hitherto jus ad vim has been discussed within the field of just war only, and international lawyers have shown little interest in it, not least because many manifestations of force-short-of-war raise profound legal questions. However, similar to other state practices that might be conceived as acts of force-short-of-war, the question of the legality of supplying weapons to Ukraine has sparked debate. Weapons transfers raise legal questions in at least five regimes of international law, namely, those of jus ad bellum; the law of neutrality; international humanitarian law; state responsibility for complicity in internationally wrongful acts; and international criminal law. Making the matter even more complex, the five legal regimes are non-hierarchical and legally independent.¹¹ In addition, some regimes seem more straightforward to judge than others. Regarding jus ad bellum, while sending weapons to Ukraine marks a use of force against Russia, doing so does not violate international law.¹² Furthermore, there are no jus ad bellum restrictions regarding the quantity or quality of weapons that western states can deliver, as long as Ukraine fights its war of self-defence lawfully.¹³ Another legal regime where most lawyers are in overwhelming agreement is international humanitarian law, in particular regarding the question of whether providing Kyiv with weapons turns the provider into a co-belligerent. Under international humanitarian law, the determinant factor of co-belligerency is the actions a particular party takes in an armed conflict. While direct participation in hostilities would meet that standard, a majority within the international law community holds that supplying weapons falls short of it.¹⁴ Unfortunately, however, some of the other legal regimes are more difficult to assess. There has been significant disagreement within the international law community, especially with regard to the law of neutrality, which has been described as ‘notoriously unclear’.¹⁵

Not surprisingly, western leaders like Scholz have emphasized time and again that their actions are both morally and legally sound. Importantly, however, the morality and legality of war are not one and the same, although they share the goal of restraining the horrors of war. Both are ‘historically conditioned realities whose development over time has come in response to differing needs in differing contexts’.¹⁶ The expansion of instances of force-short-of-war that has given rise to jus ad vim theorizing within the field of just war represents such a need. Simultaneously, the justifications provided by western governments in defence of their lethal aid to Ukraine are also shaping the legal debate. For example, it has been argued that, due to the uncertainty as to whether the law of neutrality still applies in response to acts of aggression, western support for Ukraine marks a relevant case of state practice capable of illuminating the legal state of affairs.¹⁷ In consequence, grappling with the rights and wrongs of force-short-of-war has both moral and legal relevance, as neither should be seen as ‘fixed and constant’,¹⁸ which gives emphasis to thinking about how to regulate force-short-of-war.

The article unfolds in two main parts. Firstly, I turn to the debate about the Scholz government's decision to send weapons to Ukraine. I will start by giving a voice to Scholz himself before I turn to the heated public debate his decision-making has sparked. Secondly, in light of the German conversation about the rights and wrongs of supporting Ukraine, I apply the prism of jus ad vim. I will point out how supplying weapons to Ukraine affirms key insights of jus ad vim scholarship and also highlights the vis perpetua critique. Regarding the latter, I explore the morally problematic idea of using Ukraine's war effort to attrit Russia, to reduce Putin's capacity to threaten NATO territory. Moreover, I introduce the ‘expiry date’ dilemma to the jus ad vim vocabulary: this relates to the concern that the West's support for Ukraine will prove unsustainable in the long run and thus will only delay Ukraine's defeat.

Germany's Zeitenwende and weapons for Ukraine

Exploring the morality of delivering weapons via the German debate provides unique insights due to the country's post-second World War strategic culture of military restraint and, as a consequence of it, its heated debate about supplying arms to Ukraine. The essence of Germany's foreign policy after 1945 is commonly characterized as having rested on two pillars, namely ‘Never again war’ and ‘Never again alone’. These two pillars were intended to ensure that Germany drew the right lessons from its past wars of aggression and would become a force for peace that emphasized multilateralism.¹⁹ That said, however, in the 1990s, with the challenge of a civil war along ethnic lines in Yugoslavia, a new pillar of ‘Never again Auschwitz’ was introduced and needed to be reconciled with the two earlier ones.²⁰ It is in this context that Germany had to find answers to the question of when, if at all, it would be willing to employ military force beyond the defence of its own territory and that of its NATO allies. In the decades to follow, Germany would contribute troops to numerous ‘out of area’ operations, including in Afghanistan and Mali. Despite an undeniable increase in its global military footprint, German governments have continued to emphasize the tradition of military restraint and do not commonly reference just war thinking directly.

Given this context, it is unsurprising that the return of an immediate threat to NATO territory due to Russia's invasion of Ukraine has caused a political shock wave in German politics, succinctly captured in Chancellor Scholz's reference to a Zeitenwende²¹—the dawn of a new era in German defence policy. In a high-profile speech to the national parliament (Bundestag), the chancellor announced a radical break with Germany's post-Cold War attitude towards its armed forces, the Bundeswehr, which former German president Horst Köhler (2004–2010) had once described as ‘friendly disinterest’.²² In response to Putin's war of aggression, Scholz promised an unprecedented spending boost for the Bundeswehr as well as committing to meet NATO's spending goal, to which various German governments had previously only paid lip service. Most importantly for this article, the chancellor also announced that Germany would deliver weapons to help Ukraine in defending itself against Russia. The decision to supply arms came after weeks of hesitation, for which the newly formed coalition government had both received praise and condemnation as part of an increasingly heated public debate. In the following two years, Germany would increasingly step up its military support, including the delivery of its main battle tank as well as advanced air defence systems.

Crucially, in his Zeitenwende speech Scholz indicated that German support to Ukraine could not be unlimited. After all, Ukraine was not a NATO member state and, while it was right to support its fight against an unjust attack, a direct involvement in the war had to be avoided. In Scholz's own words, a ‘major challenge lies in preventing Putin's war from spilling over into other countries in Europe’.²³ While mentioned in his speech, the challenge of avoiding being directly drawn into the war became more pronounced in a high-profile interview Scholz gave to Der Spiegel, in which he was asked about what critics saw as Germany helping Ukraine too little and too late.²⁴ As will be discussed below, Scholz's response caused a heated exchange among German intellectuals that is worth exploring, as it illustrates the split in German public opinion about the appropriate level of support for Ukraine. In the interview, besides defending his government's record of supplying Ukraine with weapons, the chancellor emphasized his intention not to get directly involved in the war. Asked what he was afraid of in his hesitancy to send more weapons as requested by Ukraine, Scholz answered with the following succinct statement that deserves to be quoted at length:

We are supplying weapons, and many of our allies are doing so as well. This is not a question of fear, it is one of political responsibility. Imposing a no-fly zone, as has been called for, would have made NATO a party to the war … I said very early on that we must do everything possible to avoid a direct military confrontation between NATO and a highly armed superpower like Russia, a nuclear power. I am doing everything I can to prevent an escalation that would lead to a third world war. There cannot be a nuclear war.²⁵

What emerges in Scholz's argument about the limits of supporting Ukraine is a prudential consideration: the threat of nuclear war as a consequence of being directly drawn into the war. While the chancellor abandoned his strict opposition to lethal aid based on a changed estimate of the likelihood of escalation, and decided to deliver advanced weapons systems, at the time of writing he still rejected certain supplies as too risky, and put restrictions on how weapons supplied by Germany could be used by Ukraine. This risk consideration has become especially pronounced, two years after the Zeitenwende speech, in the still-ongoing debate about a potential delivery of Taurus missiles to Ukraine. While key NATO countries, such as the United States, the United Kingdom and France have supplied Ukraine with their own versions of ballistic and cruise missiles, the chancellor has clearly stated that Germany will not deliver Taurus under his leadership. Apparently fearing the risk of escalation that the delivery of Taurus may cause, Scholz, against the opposition of major voices within his own party and government coalition, opposes this move. Moreover, as noted above, the German government has not allowed Ukraine to use weapons supplied by Germany to fire into Russia, with the exception of the immediate vicinity of the Kharkiv region. Another ‘no’ has been put forward by Scholz in response to Macron's argument not to draw a red line with respect to a potential future deployment of NATO troops to Ukraine.

Debating the Zeitenwende

When concentrating on the German context, it is important to note that Scholz's reasoning and his government's policies have sparked what Jürgen Habermas has called ‘a strident, media-fueled debate’.²⁶ For the purpose of this article it is worth highlighting a conversation among German intellectuals which gives further emphasis to grappling with the issues around the supply of weapons to Ukraine under the umbrella of force-short-of-war. In response to Scholz's initial decision to send weapons to Ukraine, two opposing groups of published high-profile open letters came to fundamentally different conclusions. Representing one side of the conversation, in a letter published on 3 May 2022 a group of intellectuals and artists called upon the chancellor to return to his initial position of military restraint in the conflict that ‘had so carefully considered the risks’.²⁷ While stressing that Russia's war violated international law and affirming that ‘there is a principled political and moral duty not to retreat from aggressive force without a fight back’,²⁸ the authors held that the conclusions to be derived from these assumptions had ‘limits in other precepts of political ethics’.²⁹ The most profound such limit the authors identified was the one that Scholz had also highlighted, despite his decision—rejected by the authors of the open letter—to eventually deliver weapons to Ukraine. They wrote:

First, … the categorical prohibition of accepting a manifest risk of escalation of this war into a nuclear conflict. The delivery of large quantities of heavy weapons, however, could make Germany itself a party to the war. And a Russian counterattack could thus then trigger the mutual assistance case under the NATO treaty and thus the immediate danger of a world war.³⁰

The authors explicitly warned Scholz not to make the ‘error’³¹ of assuming ‘that the responsibility for the danger of an escalation to a nuclear conflict concerns only the original aggressor and not also those who, with their eyes open, provide him with a motive to act in a possibly criminal manner’.³² The right way forward, in the eyes of the authors, would be for the German government to stop sending weapons to Ukraine and facilitate a ceasefire that would bring about ‘a compromise that both sides can accept’.³³

In response, in an open letter published the following day, another group of intellectuals advocated the exact opposite: namely, the continued delivery of weapons to Ukraine. The letter argued that a negotiated peace that would not amount to a subjugation of Ukraine could only be achieved by strengthening Ukraine's defence capability and ‘maximally weakening Russia's war fighting capacity’.³⁴ If Russia's war in Ukraine was successful, ‘the danger that the next war will take place on NATO territory will increase’.³⁵ Importantly, the authors also commented on the danger of an escalation to nuclear war. While noting that the threat of nuclear war was a part of Russia's psychological warfare, the authors stressed that they were not taking the threat lightly. However, not delivering weapons due to Russia's nuclear threats would only encourage Moscow to engage in ‘further military adventures’.³⁶ That, they argued, is why the threat of a nuclear escalation needed to be countered by a credible NATO deterrent.

As this sketch of the debate illustrates, a weighty aspect of the disagreement on the morality of delivering weapons to Ukraine has been the fear of escalation, especially to nuclear war. While they come to different conclusions, all sides—Scholz and his critics—engage with the threat of escalation. Importantly, without mentioning it, Scholz's critics foreground jus ad vim thinking in their arguments. To explain why, I turn to Habermas, who has provided a succinct analysis of the challenges Scholz is facing. Habermas, in a May 2022 essay titled ‘War and indignation’, came out in support of what he essentially saw as the chancellor's prudent decision-making. Explicitly referring to the Scholz interview in Der Spiegel, Habermas had the following to say to those who in his eyes judged the chancellor harshly: ‘And yet I am bothered by the self-assurance with which the morally indignant accusers in Germany are going after an introspective and reserved federal government’.³⁷ Pointing to a ‘risk threshold’³⁸ self-imposed by the West as a consequence of the decision not to become a party to the war, Habermas expressed his understanding of the conundrum faced by Scholz:

Those who ignore this threshold and continue to aggressively and self-assuredly push the German chancellor toward it have either overlooked or not understood the dilemma into which this war has plunged the West—because the West, with its morally well-grounded decision to not become a party in this war, has tied its own hands.³⁹

The dilemma for Scholz and the West more generally, according to Habermas, was ‘to choose among alternatives in the range between two evils—a defeat of Ukraine or the escalation of a limited conflict into a third world war’.⁴⁰ Scholz was operating within a narrow space of responsible policy options, including the delivery of weapons, which required ‘the sober consideration required for such self-limited military assistance’.⁴¹ In a nod to the chancellor's mindfulness of the risk threshold he identifies, Habermas argued that ‘the Federal Chancellor rightly insists on a politically responsible weighing [of alternatives]’.⁴²

In addition to the debate revolving explicitly around the supply of arms, Scholz's handling of the war against Ukraine has included another theoretically interesting element regarding jus ad vim. To date, Scholz has refused to state that the desired outcome of the war is a Ukrainian victory, defined as the full restoration of the country's sovereignty and territorial integrity. In a high-profile interview, the chancellor used the following framing, which seems to indicate that the outcome he imagines might be something less than complete victory: ‘Russia must not win and Ukraine must not lose’.⁴³ In a later interview, when asked about his unwillingness to use the term ‘victory’, the chancellor gave the following response: ‘I am happy for everyone to have his/her own formulation. Preventing Putin from winning this war is a lot, as we now know.’⁴⁴ While the chancellor has not specified precisely what he means with this framing, major voices within his party have suggested what would amount to a ceasefire along the front lines in eastern Ukraine. For example, in March 2024 the leader of the SPD parliamentary group in the Bundestag, Rolf Mützenich, asked his fellow parliamentarians: ‘Is it not the time to not just speak about how to fight a war but to also think about how to freeze a war and how to end it later on too?’⁴⁵

Not surprisingly, given the heated nature of the German debate, the suggestion of an outcome short of a complete Ukrainian victory has received considerable critical attention, from voices within both Scholz's governing coalition and the opposition, who firmly embrace a Ukrainian victory as the war objective.⁴⁶ From within academia, five leading German historians, all members of the SPD, succinctly summarized in an urgent letter the main concern with Ukraine not losing the war being the set objective: ‘We consider to be especially fatal the remarks by parliamentary group leader Rolf Mützenich, who has spoken of a “freezing” of the war, which would in fact mean a pacification in favour of the attacker.’⁴⁷ In other words, the critics of Scholz's position, and Mützenich's interpretation of it, worry that accepting anything less than a complete victory of Ukraine would resemble an unjustifiable rewarding of Russian aggression.

As I will show in the following part of the article, the above discussion of Scholz's position and the critical responses it has provoked foreground key aspects of the conversation about jus ad vim. Clearly, Scholz is putting a premium on what this conversation refers to as the probability of escalation. In what Habermas calls a choice between ‘alternatives in the range between two evils’,⁴⁸ the defeat of Ukraine and a regional war escalating to nuclear war, the chancellor also seems to accept a moral truncated victory as the outcome of the war. As I will argue next, taking escalation and moral truncated victory as guidelines results in a complex policy of risk management that may trigger a morally problematic regime of vis perpetua. In addition, noting the most recent experience of Afghanistan, it remains to be seen whether Ukraine's supporters will show willingness to maintain such a regime in the long run.

Expanding jus ad vim: arms for Ukraine as force-short-of-war

As indicated earlier, the call for jus ad vim has sparked a conversation within the field of just war. Seeking to push this conversation into new territory, the moral vocabulary that Brunstetter has provided in his account is instrumental when grappling with the morality of sending weapons to Ukraine. As Brunstetter rightly noted, prior to his monograph the jus ad vim conversation had almost exclusively concentrated on the use of force-short-of-war against non-state actors. By grappling with the supply of arms to Ukraine as a form of force-short-of-war, this article seeks to expand the jus ad vim literature by turning to a state-against-state practice. Upon investigation, the German approach to this question highlights the risk of escalation as well as one of the early critiques held against jus ad vim, namely, that it risks resulting in a regime of vis perpetua.

So how can the jus ad vim vocabulary illuminate the moral challenges the supporters of Ukraine have been facing? To begin with, as readily apparent in Scholz's remarks, the objective not to become a direct participant in the war has been the determining factor in the decision-making process. While Scholz has identified a moral obligation for Germany to support Ukraine with lethal weapons, the chancellor is unwilling to risk a direct war with Russia over Ukraine. Scholz is particularly concerned about an escalation of the war from a regional war to a global conflagration that may potentially trigger a nuclear exchange between Russia and NATO. In order to meet this challenge, he has advocated a prudent weighing of options regarding which weapons systems should be supplied, when they should be supplied, and how Ukraine may use those systems. In addition, in line with Germany's post-Second World War tradition of not acting alone, Germany's sending of weapons to Ukraine has been closely coordinated with Joe Biden's administration, which reportedly has had very similar debates about the limits of the support for Ukraine.⁴⁹

All of the above closely reflects the jus ad vim argument about the importance of considering the probability of escalation when deciding to use force-short-of-war.⁵⁰ Foregrounding the concern about escalation, Scholz has apparently been making what Brunstetter labels the ‘Rubicon assessment’: ‘the deliberation process to decide whether war, with all the costs and unpredictability it entails, is justified, or whether to proceed with some level of force-short-of-war instead’.⁵¹ Clearly opting for not crossing the Rubicon, the chancellor's guiding principle seems to have been the ‘strong moral penchant’⁵² captured in the probability of escalation principle to avoid the shift from vis to bellum. Scholz seems to have embraced Brunstetter's suggestion that if there is ‘a medium to high probability of resulting in war’,⁵³ uses of force-short-of-war are not justifiable. Importantly, Scholz's actions seem to reflect Brunstetter's conceptualization of the escalation principle in another respect: namely, the idea that the escalation principle is not a one-off judgement. Rather, it needs constant reassessment. Considering Germany's initial hesitancy to supply lethal aid that, step by step, has made way for the supply of advanced weapons systems, while still withholding other types of weapon and putting restriction on how the delivered weapons may be used, this seems to have been the result of a reassessment of the probability of escalation. For example, it seems fair to argue that early in the war, and under the impression of regular Russian nuclear threats, Scholz estimated the probability of escalation to be higher than when his government decided to supply its main battle tank. At the same time, as noted above, the Scholz government continues to consider supplying Taurus missiles as too risky vis-à-vis a potential escalation to war with Russia.

The need for a constant reassessment of the risk of escalation leaves unanswered the question of when, if at all, the presumption against escalation may be overridden. Brunstetter argues that there can be circumstances that merit exceptions to that presumption. Interestingly, one of the examples he provides is the case of the German Greens during the Balkans crisis in the 1990s.⁵⁴ The Ukraine context, however, is of a different nature, mainly because the stakes are much higher. Upon reflection, Scholz seems to be right when he argues that it would not be an act of responsible statecraft to move beyond Habermas's risk threshold and risk a war over Ukraine between NATO and Russia that may potentially escalate to nuclear war. That said, there are plenty of options that can be explored short of overstepping the threshold. The crux of the matter is, of course, to determine where exactly the threshold lies, and, it is worth adding, how to approach it. It would be a mistake to consider the threshold as fixed, and state leaders may want to explore ways of extending it. As the former UK chief of the general staff, General Sir Patrick Sanders, argues, the West has at times ‘overestimated’ how Russia will respond to its aid for Ukraine:

In some respects we have been deterring ourselves, because we have allowed the Russians to gain what you might call ‘escalation dominance’ where we've held back from the sort of decisive levels of support that we could have given Ukraine early on, for fear of what the Russians will do. Yet rather like a boiling frog, each time a threshold has reached where the Russians have said they will respond, they haven't.⁵⁵

Moral truncated victory in Ukraine

While Scholz takes pride in what he considers prudent decision-making on his part, he has also, at least implicitly, acknowledged one of the other main insights of jus ad vim scholarship. As Brunstetter has argued, due to the limited nature of force-short-of-war, it is unable to achieve the moral goods which a regular war may be able to bring about. Brunstetter calls this ‘moral truncated victory’:

Victory in a post vim situation is not decisive, meaning the state employing limited force does not obtain the power to impose its will over the vanquished enemy. Rather, the best one can hope for in a jus post vim context is what I call moral truncated victory: the extent to which order and justice figure into the narrow military and political achievements that might be obtained as a result of limited force.⁵⁶

In other words, force-short-of-war will not be able to fully remedy the injustice it responds to. According to Brunstetter, this ‘circumscribed nature of victory’⁵⁷ raises ethical questions that state leaders need to consider. In order that they can do that, he suggests two principles: the re-establishment principle and the containment principle. The former principle is built around the idea that force-short-of-war must go together with diplomatic efforts that seek to establish a ‘minimalist view of order’.⁵⁸ Writing in the context of what he calls ‘fragmented sovereignty’, Brunstetter is concerned that while military action will never be enough to bring about full peace, it might help to create a minimal form of order that seems morally preferable if compared to the status ex ante. Importantly, while Brunstetter's discussion of the re-establishment principle is situated within the context of international terrorism and counter-insurgency, the desire to link force-short-of-war and diplomatic efforts together has also been a facet of NATO support to Ukraine.

This has manifested itself both at a general and a more specific level. For example, in June 2024 delegations from 100 states gathered at Bürgenstock, Switzerland, to find ‘pathways towards a comprehensive, just and lasting peace for Ukraine’.⁵⁹ In the communiqué that was adopted during the summit, the signatories agreed on elements for a potential peace process, mindful that such a process was not likely to come soon—not least because to date Russia has not indicated any serious intent to stop its aggression. Besides concrete elements such as the protection of Ukraine's nuclear power plants and a guarantee for free and secure commercial shipping, the signatories affirmed the role of international law, including its elements of sovereignty and territorial integrity, as the basis for a peace process.⁶⁰ The communiqué received overwhelming support from the countries that have supported Ukraine with lethal aid, which speaks to Brunstetter's argument that force-short-of-war needs to be supplemented with diplomatic efforts.

In addition, outside the Bürgenstock format, Scholz has indicated that, while the Russian war effort currently speaks against it, he would be willing to talk directly with Putin if he felt that such talks could have an impact.⁶¹ The German government has also been active in bilateral diplomacy with regard to the war against Ukraine. Directly related to the fear of nuclear escalation triggered by repeated Russian threats, the chancellor has claimed credit for Chinese President Xi Jinping's condemnation of the use and threat of using nuclear weapons.⁶² Xi's remarks, made during a press conference with Scholz in November 2022, were commonly interpreted as a signal to Russia to step back from its nuclear sabre-rattling. Thus, it seems fair to argue that the core idea of the re-establishment principle, linking force-short-of war and diplomacy together, has been a feature of jus ad vim action in Ukraine.

The containment principle highlights the role of force-short-of-war to contain imminent or ongoing aggression, with hope that the use of force-short-of-war will provide an opening for diplomatic efforts that can stabilize or even pacify the conflict.⁶³ In Brunstetter's words, force-short-of-war ‘should be aimed at keeping evil regimes in check’.⁶⁴ In light of the above presentation of Scholz's position, the containment principle seems readily apparent. Scholz's ‘Russia must not win and Ukraine must not lose’ rhetoric, especially in the Mützenich manifestation of ‘freezing’ the war, comes across as an acknowledgement that the rationale of German weapons for Ukraine is a moral truncated victory. Scholz seems to accept that a full restoration of Ukraine's sovereignty and territorial integrity is unachievable and the best possible outcome is a containment of Russian aggression to the eastern parts of Ukraine. In other words, due to the perceived risk of escalation over the use of force-short-of-war, the best obtainable outcome is to keep Putin ‘in check’. In Scholz's own words, ‘And quickly it became apparent that this would not be a short war. We will still have to deliver weapons and munitions to Ukraine for a long time.’⁶⁵ What this way of reasoning seems to be missing, or at least not foregrounding, is the important question of authority with regard to Germany's support for Ukraine. As it stands, it seems that as long as Ukraine insists on a full recovery of its territories, and as long as Germany continues to embrace moral truncated victory, Ukrainian authority to conduct its self-defensive war against Russia will be circumscribed. As it relies so heavily on western support, the Ukrainian war effort is to a large part determined by its backers' approach to the war. This is an important moral consideration to which I will return in a moment.

Arguably, a stabilization of the war seems morally preferable if the alternative was a Ukrainian defeat that would be the result of not using force-short-of-war. However, as I will argue in the following final section, the acceptance of moral truncated victory highlights one of the most powerful critiques that has been held against jus ad vim, namely, that it can lead to a regime of vis perpetua. Once more, Habermas's lament about the chancellor finding himself caught between two equally difficult choices—a Ukrainian defeat and a potential escalation of the war—rings true.

Force-short-of-war in Ukraine: towards vis perpetua?

The concept of moral truncated victory and the re-establishment and containment principles foreground profound moral challenges in the supply of weapons to Ukraine. They also, as discussed above, suggest strategies to mitigate those challenges. However, even if successful, achieving and maintaining moral truncated victory in Ukraine will remain a morally imperfect outcome, as it is unable to achieve a just peace in the intermediate or even long-term future. In other words, weapons for Ukraine as force-short-of-war comes with the risk of perpetuating this type of force. Interestingly, this is not a new concern for jus ad vim scholarship. Writing in the context of armed drones, Christian Enemark has warned against using force-short-of-war as a method of risk management that has no end in sight. His worry is that jus ad vim may lead to a morally problematic regime of vis perpetua: ‘As the death and destruction resulting from violence are prima facie wrongs, they can begin to be legitimized by trading them away only temporarily in the expectation that the promise of a better peace will thereby be fulfilled.’⁶⁶ As the above discussion has demonstrated, Scholz, at least implicitly, seems to accept that the delicate balance between not allowing Russia to win and preventing Ukraine from losing risks perpetuating the war. Noting that a just peace forms the horizon of just war thinking, such a regime of vis perpetua seems morally problematic indeed.

In addition to these general reservations against a vis perpetua, there are two more specific aspects in the debate about weapons for Ukraine that raise ethical concerns: one points to the present, the other to the future. In April 2022 US Secretary of Defense Lloyd Austin made the following point about the rationale behind supplying arms to Ukraine: ‘We want to see Russia weakened to the degree that it can't do the kinds of things that it has done in invading Ukraine.’ He went on to specify that Russia should ‘not have the capability to very quickly reproduce’⁶⁷ the personnel and equipment it was losing in its war of aggression. In other words, Austin's remarks could be interpreted as suggesting that Russia's losses on the battlefield in Ukraine, enabled by NATO supplies, will reduce the risk of further Russian aggression, potentially unleashed against NATO member states. How is this argument relevant to the vis perpetua critique of jus ad vim? Without seeking to suggest that Austin had in mind such a policy, his remarks point in a direction that on reflection seems morally problematic. Let us imagine that NATO member states, following Scholz's framing about Russia not winning and Ukraine not losing, were to deliberately deliver just as much lethal aid as was necessary to maintain the status quo in eastern Ukraine. Put differently, they were to implement a form of Mützenich's insinuation about ‘freezing’ the war. The rationale for that would not be the careful weighing of actions aimed at avoiding the two evils Habermas has identified, but to use Ukraine's war of survival to wear down a potential future threat against NATO territory. Simply put, NATO would use Ukraine to create a regime of perpetual force to attrit Russia by the means of force-short-of-war. While such a policy would be aimed at keeping Russia ‘in check’, one of the elements of the containment principle of jus ad vim, it would do so by using the Ukrainian war effort to reduce the risk of future war with Russia. It would essentially amount to a preventive use of force-short-of-war that, like preventive war, seems irreconcilable with the just war tradition.⁶⁸

Finally, there is one more reservation about creating a regime of vis perpetua in Ukraine. It is mainly about the return of Donald Trump in 2025 as president of the United States, but also includes questions about the willingness of countries such as Germany to continue delivering weapons to Ukraine in the years to come. One could call this the ‘expiry date’ dilemma of jus ad vim. While this reservation points to the future and might not fully materialize in the end, recent history seems to ask for caution when assessing the willingness of western societies to sustain military campaigns for the long run. In particular, the recent experience in Afghanistan has sown doubts about the endurance of Ukraine's supporters to continue its lethal aid in perpetua. Consequently, moral truncated victory, due to the difficulties of sustaining a regime of vis perpetua, may have an expiry date that could lead to Ukraine's defeat and thus reward Russian aggression. And, indeed, the warning signals of not being able to sustain arms deliveries for Ukraine already seem to partly determine policy. Apparently in response to Trump's overt threats to force Ukraine into negotiations with Russia that are estimated to result in the loss of its eastern regions and thus reward Russian aggression, NATO members have been considering ways of making arms deliveries to Ukraine ‘Trump-proof’ by, for example, transferring the US-led coordination of supplies to NATO.⁶⁹ Returning to Germany's role as the second-ranking supporter of Ukraine behind the US, it needs to be said that the question of how long NATO member states will be able to maintain Ukraine's use of force-short-of-war goes beyond Trump. As the German electorate continues to be split regarding weapons for Ukraine, it seems not unthinkable that the federal election in 2025 may result in a parliamentary majority in favour of reducing German arms supplies. In fact, the Putin regime's long-term strategy for its war against Ukraine seems to rely on the calculus that the West will not be able to maintain its support for Ukraine in the years to come. In the words of the CIA director William Burns, Putin estimates that he can ‘strangle the Ukrainian economy, and wear down the European publics and leaderships, and he can wear down the United States because in Putin's view Americans always suffer from attention deficit disorder and will, you know, get distracted by something else’.⁷⁰

Conclusion

When Walzer first proposed jus ad vim he was arguing in the context of the sanctions regime against Saddam Hussein's Iraq. While jus ad vim scholarship thus started as an academic enterprise that concentrated on the use of force-short-of-war between states, the subsequent conversation quickly turned towards the ethical implications for counterterrorism practices. One of Brunstetter's rationales behind providing the first elaborate theoretical account of jus ad vim has been to also consider state-on-state action, such as the imposition of no-fly zones and limited air strikes to enforce international norms. Subsequent scholarship has picked up on Brunstetter's lead to a limited extent, but force-short-of-war comes in many manifestations, some of which bring distinctive moral questions to the fore.⁷¹ This article has grappled with one such manifestation by turning to the German debate about supplying weapons to Ukraine. It emerged that the moral vocabulary provided by jus ad vim scholarship can illuminate both the decision-making process and the justifications for this practice. In Chancellor Olaf Scholz's rhetoric, key ideas of jus ad vim, such as the probability of escalation principle and the idea of moral truncated victory, shine through clearly. In addition, the two principles aimed at mitigating the ethical compromise of moral truncated victory, the re-establishment and containment principles, were found to add a meaningful dimension for the analysis of Germany's lethal support for Ukraine. The article concluded by highlighting two important reservations that risk turning moral truncated victory, already an imperfect solution, ethically speaking, into an unjustifiable practice. All in all, what the debate about weapons for Ukraine as force-short-of-war comes down to has concisely been captured in Habermas's point that leaders like Scholz are having ‘to choose among alternatives in the range between two evils’,⁷² either Ukraine's defeat or an escalation to war with Russia. Moral truncated victory, with all of the ethical challenges it entails, seems to have been the chosen strategy to avoid either of those two evils.

Footnotes

Author notes