Introduction
Proportionality is often thought to be a necessary condition of morally permissible resort to defensive force. The proportionality of forming defensive alliances, however, is a neglected topic in the contemporary literature on the ethics of war and peace. To clarify, by “defensive alliances” I specifically mean formal associations of states in which members pool their military strength against a common enemy to deter aggression and commit to engage in collective self-defense in specified circumstances, such as when one or more of them is attacked (see Snyder 1997: 4). That the proportionality of defensive alliance formation has been overlooked is surprising because, although it is clearly distinct from resort to war in self-defense, as it may not immediately involve or ever require use of force, it has the potential to provoke rather than deter aggression and thus result in war. Indeed, as I shall argue, the decision to form or not form a defensive alliance can lead to much the same good and bad consequences as the decision to resort or not resort to defensive force. Before illustrating this point and arguing that consistency suggests proportionality should therefore also be a necessary condition of permissible defensive alliance formation, I briefly outline the condition and argue for a value pluralist understanding of it .

Following the main theoretical argument, I explore its implications by considering it in relation to John Mearsheimer’s influential but controversial account of the causes of the Russo-Ukrainian War. On this account of the war’s causes, attempts by the West and Ukraine to expand/join NATO were disproportionate because the expected harms were unjustified when compared to the alternative expected goods and harms of forgoing Ukrainian membership of NATO. This in no way implies that Russia’s aggression is just, but it does imply that the West and Ukraine are partially responsible for the war and that they acted impermissibly in attempting to expand/join NATO

Proportionality

In traditional and contemporary just war theory, proportionality, together with other jus ad bellum criteria, is generally considered a necessary condition of permissible resort to war or force short of war (e.g., see Brunstetter & Braun 2013; Fisher 2011: 73–76; Frowe 2016a; Frowe 2016b: 56–59; Hurka 2005; King 2020: 278–280; Lackey 1989: 39–43; Lazar 2017; Luban 1980: 175–176). The fundamental idea is that “use of force is proportionate when the harm done is counterbalanced by the good achieved in averting a threat” (Lazar 2017). Considerations of proportionality therefore usually involve comparing the consequences of allowing a threat to materialize against those of instead resorting to a proposed use of force (Lazar 2017). It requires weighing the harms or costs that will be suffered in the event of no response to an attack or threat, such as losses of political independence and/or territory, encouragement of future aggression, harms to civilians, and so on, against the harms that will be inflicted and averted, and thus also the goods that will be achieved, by use of force, including (but not limited to) all combatant and non-combatant casualties, the economic costs of waging war, and the protection of sovereignty (Frowe 2016b: 56; Lazar 2017). Importantly, due to the unpredictability of war, it is necessary to deal in expected consequences when making these judgments (Lazar 2017).

A straightforward judgment of proportionality can be made, first, by aggregating the harms to each side that are expected to result from non-action versus use of force, and, second, by concluding that force is proportionate only if its expected harms are less overall than those of non-action (Lazar 2017). However, this approach overlooks the moral relevance of responsibility and legitimate partiality, as well as the problem of incommensurability. As the aggressor state is responsible for the victim state’s need to employ defensive force (but not fully responsible in cases where aggression is provoked by the victim state or others), and because it seems acceptable, at least to a certain extent, for the victim state to attach greater moral importance to its sovereignty and the welfare of its citizens over those of the aggressor, use of force may be proportionate even if its expected harms are greater overall than those of non-action. This does not mean that anything goes. A nuclear strike in response to a minor infringement of sovereignty, for example, is clearly disproportionate. But it does mean that proportionality is perhaps better understood as requiring only that the expected harms of use of force do not significantly outweigh its expected goods (see Lackey 1989: 40–41; Lazar 2017). That said, the more problematic issue is that unless all of the expected harms and goods are weighted according to an ultimate moral value, such as individual well-being, or in accordance with a theory of value that specifies their relative worth, attempting to calculate proportionality seems to involve weighing incommensurable values (see Frowe 2016b: 57–59; Hurka 2005: 57; King 2020: 278; Rodin 2002: 115). Thus, assuming non-adherence to a master value or a theory of relative value, whether non-action or use of force has less expected overall disvalue appears indeterminable, as does, regarding the more permissive view, whether or not use of force entails not too much expected overall disvalue. Instead, proportionality judgments will need to be made in accordance with value pluralism and by appeal to intuitive trade-offs, that is, according to whether or not use of force involves expected gains in certain values (e.g., political independence and territorial integrity) that intuitively justify regrettable expected losses in others (e.g., individual well-being) when compared to the alternative expected trade offs of non-action. On this approach, there may be cases in which small expected gains in certain values (goods) justify large expected losses in others (harms). For example, use of force to avert an otherwise expected small loss of territory may seem justified even though it is expected to be very costly in economic terms, assuming those costs can be collectively shouldered by society without severely undermining people’s well-being. But if the large expected costs instead take the form of, say, hundreds of thousands of combatant and non-combatant casualties and/or other forms of large-scale acute suffering, then, use of force to avert a small expected loss of territory seems disproportionate.

Two final points must be mentioned. The first is that the unpredictability of war means that its proportionality can change over time. A war that begins as proportionate, because its expected goods justify its expected harms when compared to the alternative expected trade offs of not fighting, might in time become disproportionate because its harms prove to be greater than initially anticipated. For this reason, the proportionality of war, and thus the permissibility of continuing to fight, must be continually reassessed (Fisher 2011: 75; Frowe 2016b: 56–57). The second point is that even if use of force is proportionate it may nevertheless be impermissible all things considered. Just war theory stipulates a number of conditions for permissible use of force, including, perhaps most importantly, the requirement of necessity or “last resort” (see Fisher 2011: 73; Frowe 2016b: 64–65; Lazar 2017). In many cases, use of force will not be the sole option that has a reasonable prospect of averting the attack or threat. Less harmful alternatives, such as diplomacy and sanctions, or indeed the forming of defensive alliances that serve to deter aggression by counterbalancing power and threats, may have an equal or even better prospect of achieving the “just cause”. Thus, even if use of force would be proportionate, it may nevertheless be impermissible because it is unnecessary, since the good that fighting would achieve can be realized by less harmful means.

Proportionality and Defensive Alliance Formation

Now, to proceed with the main argument, the consequences of forming or not forming a defensive alliance can be the same or similar as those of resorting or not resorting to defensive force. To illustrate, first, consider the potential harms of not forming an alliance. When faced with a significantly more powerful state or alliance of states, less powerful states, assuming “internal balancing” is unfeasible (see below), can expect the costs of not forming or not joining a counterbalancing alliance to include insufficient deterrent and defensive capabilities, and thus they can expect to incur harms commonly suffered by victim states, such as losses of political independence and/or territory, if they are attacked. The extent to which such harms can reasonably be expected, and thus whether states will look to form alliances in an effort to avert or mitigate them, will depend upon the level of threat (see Walt 1985, 1987). Arguably, as the international system is anarchic, the imbalance of power in itself constitutes a threat, for whereas balance of power serves to stabilize the system and mitigate aggression, imbalance of power invites it from the strong (see Waltz 1979: 161–163). But if the opposing side happens to be not only significantly more powerful but also particularly threatening, or even if it happens to be somewhat less powerful overall but still a considerable threat, because it is proximate, strong in offensive capability and/or is thought to have aggressive intentions, then, the level of threat increases (Walt 1985: 8–13), and with it the certainty of the consequences of not forming or not joining a counterbalancing alliance.

Other potential harms of not forming an alliance have to do with “internal balancing”. In this instance, states seek to counterbalance power or threats not through forming alliances but by attempting to increase their own economic and military power (Waltz 1979: 118). Even if this is feasible, however, it may be expected to be more costly than forming an alliance. First, internal balancing may be expected to provoke more powerful states into taking action to maintain their relative advantage, including perhaps use of force against the aspiring state. Second, achieving satisfactory deterrent and defensive capabilities may well be expected to require substantial investment in the armed forces, and perhaps therefore problematic and unpopular levels of public borrowing, tax rises and/or cuts to other public services, when these financial and political costs could instead be offset by pooling military assets with other states that share in the threat.

The main benefits of forming a defensive alliance are enhanced deterrent and defensive capabilities (Snyder 1997: 43–44), and potentially therefore avoidance of the harms that would otherwise be suffered in the event of an attack, or at least increased probability of successful defense in such an event whilst incurring some degree of harm. Attempting to form or join an alliance, however, is not a risk-free course of action. Just as attempts at internal balancing may be expected to provoke powerful states into taking action to maintain the status quo, so too might attempts at “external balancing”. When faced with the prospect of less powerful states forming or joining a counterbalancing alliance, a global or regional hegemon may seek to prevent alliance formation or expansion in order to maintain its dominance. Alternatively, if the status quo amounts to a modest imbalance of power characterized by great power rivalry, the relatively advantaged state or states may seek to prevent the formation or expansion of a rival alliance in order to maintain their advantage, whilst the relatively disadvantaged state or states may do the same in order to avert a worsening of their disadvantage. Lastly, if the status quo amounts to a balance of power, then, either side may seek to prevent the formation or expansion of a rival alliance to avert the creation of an unfavorable imbalance of power.

The types of action that states might employ to prevent alliances from forming or expanding are numerous. They range from peaceful diplomacy to economic coercion to covert regime change to war that aims at the installation of a puppet regime or the annexation of territory. Whether the prospect of an alliance forming or expanding can reasonably be expected to provoke use of force, and thus whether it can be expected to result in the harms that are typically incurred by states when they are attacked by more powerful rivals, or even the extreme levels of harm that result from wars fought directly between great powers, will depend upon various factors. A key factor, again, is proximity, as the formation or expansion of an alliance on or near a great power’s borders may constitute a threat to its security and, in all probability, will at least represent a broader politico-economic challenge to its sphere of influence. Other factors include (but are not limited to) perceived and actual intentions. The formation or expansion of an alliance that is proclaimed to be defensive may nevertheless, mistakenly or otherwise, be perceived as having offensive aims by a rival, and thus as potentially warranting preventive use of force. The extent to which great powers are actually intent on competing for relative power, whether they are accepting or not of their current and projected future position, will also be of great significance. In some cases, a great power may implicitly or explicitly warn a rival that the formation or expansion of an alliance is unacceptable and that, if pushed, it will respond with force to prevent it. As discussed below, Russia’s response to the prospect of Georgia and Ukraine joining NATO is a case in point.

Now that I have clarified how it is that forming and not forming a defensive alliance can lead to much the same consequences as resorting and not resorting to defensive force, it should be evident why proportionality appears to be a necessary condition of permissible defensive alliance formation. If permissible defensive force requires that its expected harms must be counterbalanced by its expected goods, and if, as I contend, defensive alliance formation can lead to the same or similar harms and goods as defensive force, then, absent some explanation to the contrary, consistency suggests that permissible defensive alliance formation also requires that its expected harms must be counterbalanced by its expected goods.

To assess the proportionality of defensive alliance formation we need only substitute the options of comparison. Rather than compare the expected consequences of non-action against those of use of force in response to an attack or threat, we instead compare the expected consequences of not forming an alliance against those of forming an alliance in response to an attack or threat. And, in line with the above conception, rather than adopt the straightforward approach, according to which forming an alliance is proportionate only if its expected harms are less overall than those of not forming an alliance, we ought to adopt the more nuanced approach. That is to say, we ought to factor in considerations of responsibility and legitimate partiality into our assessments and, given the problem of incommensurability, judge the proportionality of alliance formation on the basis of whether it entails expected gains in certain values that intuitively justify expected losses in others when compared to the alternative expected trade offs of not allying. Furthermore, it is important to note that, as with war, the proportionality of alliances can change over time. An alliance that is proportionate when formed might in time become disproportionate because its goods turn out to be less and/or its harms prove to be more than what was reasonable to expect at the time of its formation. Thus, as with war, the proportionality of alliances, and therefore the permissibility of continuing to ally, must be continually reassessed.

Due to the varied and specific circumstances in which defensive alliances may be formed their proportionality will need to be assessed on a case-by-case basis. Nevertheless, for illustrative purposes, it is worth considering three simplified cases: (1) forming an alliance can be expected to deter aggression, whereas not forming an alliance can be expected to invite it; (2) forming an alliance can be expected to provoke aggression, whereas not forming an alliance can be expected to avoid it; (3) aggression can be expected regardless of whether the state forms or does not form an alliance. If the only expected harms are the harms that would be inflicted by aggression, and if the only expected goods are the avoidance of those harms, alliance formation is clearly proportionate in the first case, as it would then be expected to achieve only the relevant goods by deterring aggression, and clearly disproportionate in the second case, as it would then be expected to result only in the relevant harms by provoking aggression. In each case, however, there may be additional harms and goods that, if reasonably expected, must be factored into the assessment and which could alter the conclusion. In the first case, for example, allying to deter aggression is unlikely to be cost free. Perhaps the state under threat can expect alliance formation to undermine its autonomy, as its dependence on the alliance for effective deterrent capability will leave it susceptible to coercion by leading members of the alliance in regards to its domestic and foreign policies. Similarly, in the second case, although allying is expected to provoke aggression, it may also be expected to realize important goods. For instance, perhaps allying is expected to enable a successful defense as well as long-term political and economic goods, such as increased security and more profitable trading relationships. Whether these additional expected harms and goods alter the proportionality of allying in either case depends on their degree, as well as the degree of the expected harms that would be inflicted should aggression be invited or provoked. For example, if aggression is expected to cause deaths in the hundreds of thousands, incurring a small loss of autonomy is unlikely to render allying disproportionate in the first case, whilst the long-term political and economic goods of allying in the second case may not be large enough to consider it proportionate. Finally, in the third case, where aggression can be expected regardless of alliance formation, proportionality will depend on whether allying can be expected to enable a successful defense, and whether achieving that good justifies the expected harms that will be suffered and inflicted in repelling aggression. It could be that allying is a “last resort”, the only option available to the state that has any prospect whatsoever of achieving its defense. But if allying cannot be expected to repel aggression, if it has no “reasonable prospect of success”, or if success can be expected only at a cost that is too high in lives and suffering, then, allying is disproportionate and the state ought not to fight.

Proportionality and Mearsheimer on Ukraine

NATO enlargement in regards to prospective Ukrainian membership, depending on how one interprets the causes of the Russo-Ukrainian War, is possibly a case in which seeking to expand/join an alliance was disproportionate because it should have been expected to provoke Russian aggression that would result in unjustifiable levels of harm. The conventional view of what caused the war, at least in the West, centers on the idea that Putin so regrets the collapse of the Soviet Union that he has become intent on forging a new Russian empire (e.g., see Fried & Volker 2022; Neuman 2014; Ridgwell 2015). However, this view is contested, most famously by the neorealist international relations theorist, John Mearsheimer (see also Kissinger 2014; Walt 2014). In his widely cited Foreign Affairs article from 2014, as well as in his corresponding lecture to University of Chicago alumni in 2015 that has since gone viral, Mearsheimer argues that Russian aggression was provoked by the misguided policies of the West. Following Russia’s full-scale invasion of Ukraine, this remains his view (see Mearsheimer 2022a, 2022b).

According to Mearsheimer, the war’s root causes are three Western policies that are constitutive of a “strategy to move Ukraine out of Russia’s orbit and integrate it into the West” (2014: 77). The first policy and central element of this strategy is NATO enlargement, whilst the second and third policies are EU expansion and democracy promotion (Mearsheimer 2014: 77–80). The causal significance of NATO enlargement, Mearsheimer contends, is evident in Russia’s response to the 2008 Bucharest Summit. At Bucharest, the alliance considered further eastward enlargement following two previous rounds of expansion in 1999 and 2004. The Bush administration pushed hard for Georgia and Ukraine to join the alliance. However, Germany and France opposed the move, in part because of concerns about Georgia’s and Ukraine’s internal politics, but primarily to avoid unduly antagonizing Russia and risking the balance of power in the region (Mearsheimer 2014: 78; Reuters 2008; Williamson 2008). Consequently, Georgia and Ukraine were not invited to begin the formal admittance process. However, the alliance did endorse these two countries’ aspirations and it publicly declared that they would become NATO members (Mearsheimer 2014: 78–79). Putin’s response, Mearsheimer argues, was unequivocal: he insisted that the admittance of Georgia and Ukraine “would represent a ‘direct threat’ to Russia”; he was reported to have “‘very transparently hinted [to Bush] that if Ukraine was accepted into NATO, it would cease to exist’”; and later that same year, in a precursor to what would happen in Ukraine, Russia invaded Georgia in support of South Ossetian and Abkhazian separatists (Mearsheimer 2014: 79). Despite these clear warnings, Mearsheimer points out that NATO never publicly ruled out Georgia and Ukraine joining the alliance (2014: 79). Moreover, he argues that the West continued to assimilate Ukraine by integrating it into the EU economy via the EU’s Eastern Partnership initiative and by promoting democracy in the country through its funding of pro-Western individuals and groups (Mearsheimer 2014: 79–80).

With the West and Russia competing for influence in Ukraine, the situation eventually came to a head in February 2014. After months of anti-government protests that were triggered by Yanukovych’s decision in November 2013 to reject an economic deal with the EU in favor of a rival deal with Russia, Yanukovych was ousted and a new anti-Russian, pro-Western and US backed government came to power. Putin’s response, Mearsheimer argues, “should have come as no surprise” (2014: 77). He annexed Crimea, thereby ensuring that the Russian leased naval base in the port of Sevastopol would not in future fall into NATO’s hands (The University of Chicago 2015), and he backed the pro-Russian separatist groups in the eastern regions of Donetsk and Luhansk, “making it clear that he would wreck Ukraine as a functioning state before he would allow it to become a Western stronghold on Russia’s doorstep” (Mearsheimer 2014: 82).

A forceful response of this kind should have been expected, Mearsheimer contends, not only because of Russia’s response to Bucharest but also because of the logic behind it. As he rightly points out, “great powers are always sensitive to potential threats near their home territory” and Ukraine in particular is of “enormous strategic importance to Russia” because it functions as a “buffer state” between it and the West (Mearsheimer 2014: 82). As such, he insists that “[n]o Russian leader would tolerate [… NATO] moving into Ukraine”, just as no US president would tolerate, say, a powerful Chinese led military alliance moving into Canada or Mexico (Mearsheimer 2014: 82).

Of course, Mearsheimer’s account of the war’s causes is strongly contested (e.g., see Bailey 2023; Lebow 2022; Motyl 2015; Specter 2022). However, for the sake of exploring its ethical implications, let us assume that Mearsheimer is correct, specifically in his assertion that the West’s strategy to assimilate Ukraine should have been expected to provoke Russian aggression. Furthermore, let us also assume, as a logical extension, that Ukraine’s renewed pursuit and prioritization of NATO membership following the annexation of Crimea and the outbreak of fighting in the Donbas, together with NATO’s reiteration at the 2021 Brussels Summit that “Ukraine will become a member of the Alliance” (North Atlantic Treaty Organization 2021), should have been expected to provoke an escalation of some kind. For these attempts to expand/join NATO to have nevertheless been proportionate, the expected gains would have needed to intuitively justify the expected losses when compared to the alternative expected trade offs of not seeking to ally. And this, it seems to me, was unlikely to have been the case.

Until recently it would have been unreasonable to expect Ukraine to defeat Russia in a conventional war. This is evident in the expectations of military experts in the early days of Russia’s full-scale invasion, when Russia was expected to succeed in its attempt to march on Kyiv and install a puppet regime, even though Ukrainian resistance was expected to make it difficult for Russia to occupy the entire country and maintain long-term control (e.g., Sky News 2022). Expectations began to shift only after Ukraine incredibly won the Battle of Kyiv, and after the West demonstrated a surprising amount of unity and strength in its response that has included enormous military assistance. Thus, prior to these extraordinary events, attempts by the West and Ukraine to expand/join NATO should have been expected to provoke Russian aggression that, due to Russia’s significant advantage in conventional military power, Ukraine would have stood little chance of repelling, at least in the short term. After the Russo-Georgian War and prior to the annexation of Crimea, it would have been reasonable to expect Russian aggression to result in more or less what it did; large Ukrainian territorial losses at the cost of thousands of Ukrainian, separatist and Russian casualties. And, post-annexation of Crimea up until the full-scale invasion, it was reasonable to expect any large-scale offensive by Russia to result in at least some further loss of Ukrainian territory, together with the inevitable casualties, infrastructural damage, displaced persons, cyber attacks and war crimes.

In brief, the expected harms of attempting to bring Ukraine into NATO were severe. The expected goods, on the other hand, were negligible. Prior to the full-scale invasion, Ukraine was of little strategic importance to the West, hence its initial weak response to the annexation of Crimea (Mearsheimer 2014: 88; see also Walt 2014). Ukraine has since acquired greater importance to the West only because it has avoidably been made into an arena where great power rivalry and contestation of the future world order is being played out. Besides, the West could not have reasonably expected to assimilate Ukraine without provoking preventive action from Russia. As for Ukraine, if it prevails, which at the time of writing remains uncertain, it may achieve goods in the long term that serve to counterbalance the harms it has suffered, including defense of its political independence and territory, as well as other political, economic and security benefits of closer relations with the West. But, for the above reasons, when Ukraine chose to renew its pursuit of NATO membership following the annexation of Crimea these goods could not have been the reasonably expected outcome.

If the West had not sought to assimilate Ukraine, would the expected consequences have been better or even worse? As it was reasonable to expect attempted assimilation to provoke Russian aggression, an expected good of restraint would have been its avoidance. However, considering Ukraine’s strategic importance to Russia, it would have still been reasonable to expect Putin to seek to influence and manage it, even in the absence of competition for influence from the West. In defense of the West, then, it could be argued that if it had not sought to assimilate Ukraine it would have left the door open to Russian imperialism and that in those circumstances it would have been reasonable to expect Ukraine to fall into vassalage. But this outcome is not obviously worse than the alternative. Depending on the degree to which Ukraine would have been expected to lose its autonomy, this expected outcome might have been better or worse, in terms of an intuitive trade off of the relevant values, than what should have been the alternative expected outcome of an initial provocation of Russia, namely, large Ukrainian territorial losses and thousands of casualties. Intuitively, the expected loss of autonomy from non-action would have needed to be substantial to outweigh the alternative expected harms of attempted assimilation, and, at least on Mearsheimer’s view, it is doubtful that Putin would have sought to dominate Ukraine to that extent if there had been no risk of losing it to the West.

Moving forward in the timeline of our counterfactual, what if the West had attempted to assimilate Ukraine, thus provoking Russia’s annexation of Crimea and its assistance to separatists in the Donbas, but the West and Ukraine had acted differently in response? What if, as proposed by Mearsheimer (2014: 87–89; The University of Chicago 2015), the West had responded by publicly ruling out Ukrainian membership of NATO, whilst Ukraine, rather than chasing NATO membership, had instead accepted the loss of Crimea and pursued a policy of non-alignment? The obvious objection here is that such a response would have amounted to appeasement and that, given the lessons of Munich, it would have been reasonable to expect it to invite further aggression. This objection, however, assumes that appeasement always encourages aggression and implies an equivalency between Hitler and Putin that Mearsheimer rejects; he sees Putin as a rational leader who has been provoked into taking action to protect Russia’s core strategic interests, not as a madman hell-bent on territorial expansion. On Mearsheimer’s account of the war’s causes, although there was never any prospect of Putin returning Crimea, there was a fair chance he would have agreed to a plan aimed at transforming Ukraine into a neutral buffer state rather than risk the dangers of escalation and the possibility of losing it to the West. This would have cost Ukraine territory and a degree of unfreedom in its foreign affairs but achieved the considerable goods of securing its relative autonomy and averting the expected harms of escalation.

In response to the implication that it was disproportionate for the West and Ukraine to attempt to expand/join NATO, it has been suggested to me that the above assessment does not give sufficient weight to the factor of responsibility. According to this objection, even though attempts to ally should have been expected to provoke Russian aggression, Russia alone is responsible for the resulting harms and the implication that Ukraine, in particular, acted impermissibly amounts to victim blaming. I agree that considerations of responsibility ought to be factored into proportionality assessments, which is evident from the conception of proportionality I have advocated. However, as it was reasonable to expect that attempts to ally would provoke Russia, it is implausible to claim that the West and Ukraine bear no responsibility for the harms Russia has inflicted. As Helen Frowe and David Rodin both recognize, “we are morally responsible not only for harms that we directly cause but also for harms that we foresee we will trigger others to cause” (Frowe 2016a: 121; see Rodin 2014).

To illustrate, Frowe argues that it is clearly impermissible for Victim to resist being pinched by Bully if Victim foresees that his resistance will cause Bully to kill Friend in a fit of rage, because the potential good is greatly outweighed by the expected harm (2016a: 121). Such “mediated harms”, that is, harms that are triggered by an agent but which are mediated through the agency of another, count less than directly inflicted harms when judging the proportionality of defensive force, but they do still count (Frowe 2016a: 121; Rodin 2014: 82–83). Thus, mediated harms can render self-defense and, so I contend, defensive alliance formation impermissible. Furthermore, Rodin argues that the permissive effect of mediated harms, that is to say, that they do not count against the permissibility of defensive force as much as directly inflicted harms, is often overridden by the restrictive effect of duties of care (2014: 83–85). Potential victims of mediated harms are “typically people who are bound to us by relationships of loyalty, community, and kinship …, [they are] ‘our people’ …, our comrades in arms, our family members, our neighbours” (Rodin 2014: 83). As such, when states are considering employing defensive force, a duty of care applies that effectively negates any discount on mediated harms when calculating its proportionality and which, for Rodin, requires citizens not to endanger their fellow citizens’ vital interests (life, bodily integrity, freedom from slavery, and residence) for the sake of defending lesser interests (territory, resources, and political independence) (2014: 79–88; for criticism, see Frowe 2014: 123–161).

The fact that the expected harms of attempts to expand/join NATO were predominantly mediated (but far from entirely mediated as they include foreseen casualties and other harms directly inflicted by Ukraine) does not mean that the West and Ukraine bear no responsibility for them, nor does it alter the conclusion that their attempts to ally were disproportionate. As discussed above and as summarized below, such attempts should have been expected to result in severe harms and few if any goods, whereas forgoing Ukrainian membership of NATO and pursuing non-alignment should have been seen to have had a good chance of securing substantial goods whilst largely averting further harms. Thus, even when factoring in the discount on mediated harms, the expected harms of attempts to ally still clearly outweighed the lack of expected goods, and pursuing alliance formation was reckless and unjustified when it was reasonable to believe that an alternative course of action would probably result in a far better outcome.

In addition, if the discount on mediated harms can effectively be canceled out by duties of care, as seems plausible, Ukraine’s pursuit of NATO membership post-annexation of Crimea appears especially disproportionate. If citizens must not endanger their fellow citizens’ vital interests for the sake of defending lesser interests, this duty of care ought to apply not only when considering the proportionality of defensive force but also the proportionality of defensive alliance formation. Moreover, if the state in question is sufficiently democratic, and if the decision is not put to a referendum, there is good reason to think that the primary duty bearer is the government or parliament. For in those circumstances, the decision about whether or not to pursue an alliance will not be made directly by the citizenry. Rather, it will be made by citizens’ elected representatives, and thus by those who have been collectively authorized by citizens to make decisions on their behalf and in their best interests. In this light, the policy of Ukrainian governments to chase NATO membership post-annexation of Crimea, as well as the Ukrainian parliament’s decision to pass a constitutional amendment that commits the country to this goal, can be viewed as breaches of duty. For as I have argued, at the time when they were made, these decisions could not have reasonably been expected to secure Ukrainian citizens’ lesser interests in political independence and territory. On the contrary, it would have been reasonable to expect them to only further endanger these lesser interests as well as citizens’ vital interests in life, bodily integrity and residence.

Conclusion

As mentioned at the outset, the ethics of military alliances is under-theorized. Considering the impact that alliances can have in deterring, provoking and deciding wars, and their relevance to the war in Ukraine and the future of US-China rivalry, more attention needs to be given to the ethical issues that surround them. By considering the permissibility of forming defensive alliances I hope to have contributed towards addressing this deficit. Drawing on the jus ad bellum criterion of proportionality in just war theory, my central claim is that, if permissible defensive force requires that its expected harms must be counterbalanced by its expected goods, then, permissible defensive alliance formation seems to also require that its expected harms must be counterbalanced by its expected goods, since the latter can result in much the same consequences as the former. Moreover, considering the incommensurability of values in play when making proportionality judgments, I have argued for a value pluralist understanding of the criterion. On this view, defensive alliance formation is proportionate if the expected gains in certain values (goods) intuitively justify the expected losses in others (harms) when compared to the alternative expected value trade-offs of not allying.

To illustrate and explore the implications of my theoretical claims I considered them in relation to Mearsheimer’s influential account of the root causes of the Russo-Ukrainian War. On this account, the West’s strategy to assimilate Ukraine and later Ukraine’s renewed pursuit of NATO membership were disproportionate because the expected harms were unjustified when compared to the alternative expected goods and harms of forgoing Ukrainian membership of NATO. Attempts by the West and Ukraine to expand/join NATO should have been expected to provoke Russian aggression/escalation that would result in large Ukrainian territorial losses, thousands of casualties and various other harms. The expected goods, on the other hand, were negligible. Prior to the 2022 escalation, Ukraine was of no great strategic importance to the West, and Ukraine’s decision to chase membership post-annexation of Crimea could not have reasonably been expected to yield the goods that Ukraine may now achieve from a military victory. In comparison, not attempting to expand/join NATO should have been expected to result in, or at least should have been seen to have had a reasonable prospect of achieving, more justifiable trade-offs in autonomy, territory and well-being. If the West had never sought to assimilate Ukraine, it would have been reasonable to expect this to achieve the good of not provoking Russia, and thus avoidance of the considerable expected harms of doing so, but at the cost of leaving Ukraine open to Russian imperialism and therefore some (but probably not an unacceptable) degree of lost autonomy. And, later on, if the West had responded to the annexation of Crimea by ruling out Ukrainian membership of NATO, whilst Ukraine had responded by adopting a strategy of non-alignment, there was a reasonable prospect, which was logically deducible at the time, that this would have achieved the immense goods of averting escalation and securing Ukraine’s relative autonomy, at the cost of Ukraine having to concede already lost territory and accept constraints on its relations with the West.

 

Finally, I wish to reiterate that nothing argued herein is meant to imply that Russia’s aggression is just. On the contrary, Russia’s actions fail to satisfy multiple jus ad bellum criteria. But this in no way rules out the possibility, as the theory developed and applied herein does imply, that the West and Ukraine are at least partially responsible for the war and that they acted impermissibly in attempting to expand/join NATO.