Revising, or Rejecting, ‘Reasonable Prospect of Success’ in Just Wars? Lessons From Ukraine

Rhiannon Neilsen
Wednesday, March 22, 2023, 2:08 PM

At the outset of the invasion, analysts doubted Ukraine’s likelihood of winning a war against Russia. But as the conflict enters its second year, Ukraine’s resistance prompts a challenge to conceptions of “just war” and conditions of “success."

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“It’s a victory when the weapons fall silent and people speak up.” Since Russia’s invasion in February 2022, Ukrainian President Volodymyr Zelenskyy has been especially vocal about victory —and glory—for Ukraine. As Zelenskyy put it, his people will fight “whatever the cost.” The cost so far, according to the U.N. Office of the High Commissioner for Human Rights, is 18,000 Ukrainian civilian casualties and up to 13,000 Ukrainian soldiers killed. As of February 2023, the U.S. estimates 200,000 dead or wounded Russian soldiers, but that figure may be as high as 270,000.

As well as the discourse surrounding victory, the war has been soaked with references to ethics and justice. U.S. President Joe Biden, for one, has claimed that support for Ukraine is “a profound moral issue” and “the right thing to do.”

But as the tanks first rolled across the border a year ago, Ukraine’s likelihood of defeating Russian aggression was considered remote. Most analysts expected a swift Russian take-over, seemingly doubting the smaller state’s willingness to fight, let alone triumph. Russia’s military ostensibly dwarfed Ukraine’s. Kyiv was forecast by experts to fall within the week. Two days after the invasion, world leaders urged Zelenskyy to leave and offered him a way out—to which he famously retorted, “I need ammunition, not a ride.” In other words, in the very early days, Ukraine did not seem to have a foreseeable prospect of success—or, to put it plainly, a reasonable chance of winning the war.

According to the prevailing moral precept by which wars are judged, the just war tradition, Ukraine would not have satisfied all jus ad bellum criteria at the start of Russia’s invasion. To permissibly resort to war, jus ad bellum requires states to have a “just cause” (such as self-defense), possess a “legitimate authority,” ensure war is a “last resort” and necessary, satisfy “proportionality,” be motivated by a “right intention,” and have a “reasonable prospect of success.” This last criterion is understood as a reasonable chance of victory. This seems intuitively coherent enough: Why put soldiers (on both sides) and civilians through needless suffering and bloodshed if there is no sound chance of winning? According to just war revisionists, even if the war is one of self-defense (as is the case with Ukraine), if it is unlikely to succeed, pursuing such war is morally prohibited. The satisfaction of the “success” criterion, for revisionists, is necessary for going to war. Just war traditionalists, however, regard the success criterion as prudential: It is not required, but it should “be taken into account in the decisions of statecraft.” For the traditionalists, self-defense could, in other words, overrule the need to have a decent chance of winning.

The war in Ukraine mounts a challenge to just war thinking, especially for revisionists but also for traditionalists. Specifically, the war highlights the urgent need to revise the success criterion beyond the logic of winning versus losing (particularly if it is a necessary condition in jus ad bellum, as per the revisionists). More forcefully, the war in Ukraine prompts a possible rejection of the success criterion altogether. In some ways, this view seems to echo the traditionalist approach; that is, success is a tertiary consideration and can be set aside should there be a strong enough just cause, as in Ukraine. But if, according to traditionalists, success can be so quickly ignored upon satisfying a just cause, then why include it in jus ad bellum in the first instance? Its inclusion in just war calculations is seemingly neither necessary (as per the revisionists) nor prudential (as per the traditionalists). Such lessons from Ukraine have profound implications for political leaders deciding whether to wage war. 

The Logic for a Reasonable Chance of Success in Just Wars

The whole point of the success criterion—of having a decent chance of emerging victorious—is to privilege the preservation of human life. Its role in just war thinking is intended to avoid wanton killing, emotional and psychological turmoil, and widespread economic damage. This applies to combatants and noncombatants on both sides.

According to revisionists, if Ukraine did not seem to have a reasonable prospect of success, it should not have resorted to a war of self-defense in the first instance. Helen Frowe, a revisionist, believes that it is wrong to send soldiers into a war that will “very likely end in defeat, with all the loss of life and injury that defeat will entail” for both sides. To come to this view, Frowe applies an individualist account to war: The moral standards and assessments that apply to individuals are the same as those in war (war is not morally exceptional). She concludes that satisfying the success criterion is a moral requirement when deciding whether to wage war, because (following the individualist account) “it would be wrong for an individual to use likely futile self-defence if doing so exposed bystanders to significant harm.” Because many analysts regarded Ukraine’s chances of success—of entirely beating Russia—as minimal, revisionists would have ostensibly considered the resort to a war of self-defense unjust.

Curiously, success was not part of the original conceptions of just war as conceptualized in the Christian tradition set forth (largely) by St. Augustine and (later) St. Thomas Aquinas. “Success” became incorporated in modern conceptions of jus ad bellum alongside “last resort” and “proportionality.” Unlike revisionists, traditionalists view just war theory less as a checklist and more as guiding principles for the practicalities of war. This is especially the case when it comes to what Michael Walzer regards as “supreme emergencies”: Where the survivability of the state hangs on the line, “the on-goingness of the community is at stake,” or failure to resist means “communal death.” If all other jus ad bellum criteria are met, then there is a “presumption in favor of permitting some kind of armed response,” even if the odds of military success are small. Attempting to win is morally justified because of how much there is to lose. Perhaps no 21st century case demonstrates this so acutely as the war in Ukraine. As Brian Orend explains, the condition is still “important”: Contemplating success is “the least, we might say, [the victims] owe themselves.” In other words, the victims would do well to weigh whether the anticipated large-scale carnage is, put bluntly, worth it, given the unlikelihood of victory.

The fighting and dying in Ukraine, however, challenges revisionist and traditionalist approaches to just war in two ways. First, if “success” is to remain a condition in jus ad bellum, then it should be redefined beyond strictly winning the war. Second, and stronger still, given the opacity of a war’s course, perhaps “success” should be rejected from jus ad bellum altogether—both as a necessary (as per revisionists) and prudential (as per traditionalists) condition. 

Revising “Success”?

If revisionists are committed to retaining a “success” requirement as an inexorable part of jus ad bellum, then the conflict in Ukraine provides compelling reasons to include outcomes that go beyond such a narrow scope. Consider the message that arises from engaging in war: No matter the outcome of the war in Ukraine, success may constitute a “signpost” in the international system that imperialistic ambitions will not be without consequence. Further, success may plausibly qualify as simply weakening the enemy. The rouble has plummeted and Russia’s military suffered severe knock-backs—so much so that Russian conscripts are being sent to the front line with little training and World War II rifles. Russian President Vladimir Putin appears to be fighting a war of attrition. He is assuming that the international community underestimates just how many Russian bodies he might deploy and overestimates how much he cares about Russian lives. But the longer Putin insists on fighting, the more damage is being inflicted on Russia’s military, economy, and (unfortunately) people. Even if Putin were to “win,” the consequences of the war—notably, Ukraine’s resistance—have been dire for Russia. A weakening of Russia’s (potential) international influence qualifies as a “success."

At the same time, “success” might include strengthening alliances and international commitments to upholding the liberal democratic order. Since the invasion, NATO has been invigorated, and Finland and Sweden have officially applied to join. Even states that have been historically neutral have joined the European Union in filing sanctions against Russia. If anything, despite recent years of political polarization, there is a fervent flare in states uniting to condemn violations of international peace and security. Galvanizing international solidarity around liberal democracy can be thought of as another kind of success.

A further potential view of success is Ukraine retaining most, if not all, of its sovereign autonomy. A successful end to the war might be Russia having been pushed back enough, though not completely. Early on, Zelenskyy himself stated he would “consider it a victory for our state, as of today, to advance to the Feb. 24 line without unnecessary losses.” In May 2022, Henry Kissinger controversially called for Ukraine to cede territories to Russia, advocating for a “return to the status quo ante.” His statements were geared toward limiting any more slaughter. As of December 2022 (with the war increasingly in Ukraine’s favor), Zelenskyy now maintains that the restoration of all Ukrainian territories is “not up for negotiation.” On Feb. 24, 2023, he claimed that Ukraine is “ready for anything. We will defeat anyone.” But, as Zelenskyy’s remarks from earlier in the war demonstrate, ceding some territory to Russia was a consideration. And experts still consider the full restoration of territorial integrity to be a “highly unlikely outcome.”

When weighing whether to take up arms in self-defense, a wronged state might also consider a frozen conflict to be a kind of success, especially in the event that the war will not officially terminate and both sides pursue peace talks. A likely stalemate is, of course, a more morally justifiable success over that of prolonged war with unending death and destruction. This is especially the case if it seems a formal peace treaty (even from the outset) appears unlikely. In addition to a stalemate, such a foreseeable success may plausibly take the form of a cessation of hostilities, or cease-fire. Alternatively, an armistice (which “ended” the Korean War and has held for 70 years) may qualify as success.

Sometimes having a reasonable prospect of success will only increase once war has begunas in the case of Ukraine. The West, prior to affordances of aid, was unduly skeptical of Ukraine’s resistance. But Zelenskyy stayed. NATO rallied. Ukrainian morale dominated. Tanks were sent.

And yet, according to a revisionist interpretation of just war, if there is no reasonable chance of success, such a war should not have begun in the first place. There is a tendency to be wrong about the anticipated outcome of war. Putin, for one, was overly optimistic. Russia clearly inflated its military power (a product of sustained information and online psychological operations, where it lied to itself and the world about its capabilities). It underestimated the political morale of its combatants to fight. Bravery is about taking the risk, about doing what is (morally) right, without knowing, with any degree of certainty, that you will succeed. Just that there is a chance, however slim.

As James Childress notes, “Success … may be broader than victory.” Of course, the worry is that if we start allowing for “success” to mean anything, it becomes a catch-all term, suited to be applied retroactively with hindsight bias. A year of fighting in Ukraine, however, forces us to at least rethink the just war tradition conception of success away from the zero-sum logic of winning versus losing.

In short, if success is to be a necessary condition in jus ad bellum, as per the revisionists, then what constitutes success ought to be renegotiated. Ukraine highlights that the revisionists’ requiring a reasonable chance of winning in just war deliberations is too strict.

Perhaps it is unwise, implausible, superfluous, or even dangerous to demand a reasonable prospect of success in jus ad bellum as necessary or prudential. This poses a challenge not only to revisionists but also to traditionalists. It makes little sense for success to be even a tertiary consideration, as per the traditionalists, if it can be simply set aside in the face of “supreme emergencies” like in Ukraine. After all, how can anyone ever truly know whether there is a sufficient prospect of success when the fog of war is so notoriously thick? 

Rejecting “Success”? 

Despite uncertain beginnings, Zelenskyy’s forces continue to fight with tenacity and gain ground over Russian held-territories. While revisionists would retort that the resort to war without success is unjust, traditionalists see it as something victims would do well to contemplate. But, because it can be quickly overridden (in light of just cause), success for traditionalists seemingly does not sway the moral justifiability of that war. So maybe success should not be part of just war assessments at all. In addition to the potential need to revise “success,” then, the Ukraine war also raises the question of whether success (as a necessary and prudential condition) should be rejected in jus ad bellum entirely.

As battles across Ukraine (in places like Bakhmut and Kharkiv) illustrate painfully, civilians stand to gain—and lose—from this war in Ukraine. Obviously, civilians ought to be afforded immunity in war—something Russian soldiers are flagrantly violating, as evidence of war crimes pile up. Yet it is wrong to construe as mere bystanders civilians of a state being subjected to unjust harm. Civilians are, by definition, the victims on whose behalf armed forces willingly fight. In the same way civilians not only stand to lose should their militaries not fight, they stand to gain (that is, weakening the enemy, retaining most of their autonomy, signaling that invasions will not be without consequences) even if there is very little reasonable prospect of fully winning the war. Once civilians are seen as beneficiaries on whose behalf war is waged, then the focus is on those civilians who consent to fight, die, and survive the invasion. Given the number of Ukrainian civilians who have volunteered to fight in the ongoing conflict, it’s clear that there is a political and public intention to resist. If potential wars of self-defense are without a reasonable chance of success, and yet the population still wants to fight, is this not their right to decide for themselves? Based on the Ukrainian civilians’ eagerness to defend their homeland, and the toll the war has taken on their lives, why must there be a reasonable prospect of success?

If a state appears to have no reasonable chance of success and were to surrender in the face of (what appears to be) a vastly more powerful state, this may send a signal to that aggressor that neighboring states will likely do the same. The outcome of unchecked aggression may, in effect, embolden the unjust aggressor to invade other states. Indeed, Putin might have turned his sights to another former Soviet state, Kazakhstan, had Ukraine capitulated. Or a rapid surrender might suggest to other aggressor states that their imperialistic advances will go unchecked if they forcefully invade smaller states elsewhere in the world. This also has implications for rebellions against unjust regimes: If a rebellion appears to have no reasonable chance of succeeding, does this mean any violent resistance (which otherwise satisfies the jus ad bellum criteria) is unjust?

As mentioned earlier, wars of self-defense that lack a foreseeable victory at the very least send the message that unjust wars will be challenged. It will be costly—reputationally, economically, politically, and in terms of bloodshed—for the unjust aggressor, no matter if the victim state has a foreseeable chance of emerging triumphant. Surely unchecked aggression is always more disconcerting. So it is unclear why “success” must be included in jus ad bellum (as necessary or prudential) to begin with.

Further, assessments regarding whether a state satisfies the success criterion seemingly account for only material factors. Such assessments look at military prowess, economic resources, technology, operational experience, and grand strategy. In doing so, there is minimal attention afforded to the heart, morale, and support (lethal and otherwise) from one’s allies that often arise once the war has begun. There are so many intangible factors that can powerfully sway the outcome of war: The charisma of those who lead. The bravery of those who fight. The steadfast support of civilians. The $50 billion of lethal aid from the United States ($75 billion in total). How can any conception of success at the dawn of war entirely account for these factors? Focusing only on the military might send the message that nonpowerful states or rebel groups should not even try to resist unjust oppression. This seems wrong.

A perverse consequence of relying on military advantage is that it may motivate states to invest in, develop, or retain even more powerful weapons—perhaps even nuclear arsenals. This is so that there is no second-guessing their prospect of success (however disproportionate or ghastly this may be). As one year of fighting in Ukraine demonstrates, there are many factors that can sway the odds in the defending party’s favor as the war unfolds. As such, must there be a requirement to give even nominal consideration to foreseeable success prior to taking up arms? Both revisionists and traditionalists might do well to simply set aside such a condition altogether.

The success criterion exists to privilege the preservation of human life. But this dangerously assumes that peace will ensue should the wronged party choose to surrender without a fight. There is no guarantee that the invading forces will refrain from engaging in mass systematic killing, even if the wronged state bows without attempting to fight back. As in Ukraine, there is evidence of Russia forcibly transferring children away from families (which satisfies the 1948 genocide convention), committing extrajudicial killing of at least 441 civilians near Kyiv, targeting hospitals and children’s playgrounds, and covering up mass graves and mass rapes. Who is to say that living under an oppressive autocracy is not a fate worse than death? Who is to say that there won’t be widespread executions or forced labor camps following an unconditional surrender?

A common refrain is “war is hell.” If this is true, and the very existence of the state hangs in the balance, as with Ukraine, then perhaps just war thinkers should simply say “to hell with success.” 

The Weight of (Winning) War in Ukraine 

The war in Ukraine brings to the fore the grim reality of just war revisionists demanding victims of unjust aggression not to fight if there is no reasonable prospect of success—or, more concretely, victory. To revisionists, failing the success condition means that it is not only morally repugnant but morally wrong to fight to defend one’s homeland. There seems to be something deeply troubling with this logic. Traditionalists, in contrast, encourage victims to ponder the gravity and gore of war in light of little foreseeable success. But they are then quick to relegate the “success” moral criterion if there is a weighty enough just cause.

Ukraine therefore prompts two reflections for just war. First, perhaps it is time to reconsider what constitutes success when going to war. If success must remain a criterion, as per the revisionists, then its definition ought to extend beyond victory. States may foreseeably meet the success criterion if the anticipated outcome is, for instance, a stalemate: It confronts an unjust act without the stringent requirement to win.

Second, it is unclear whether political and military decision-makers ought to give any credence to the success criterion when deciding to wage war. Success, to traditionalists, is a supplemental consideration, especially in the case of self-defense, like in Ukraine. The criterion seems simply to serve as a question for victims to consider when deciding whether to defend themselves: “Your chances are slim, so are you sure?” The response does not appear to impact the moral permissibility of the war. The conflict in Ukraine thus prompts a possible rejection of “success” from jus ad bellum entirely—both as a necessary (per revisionists) and prudential (per traditionalists) criterion.

There is, of course, such a thing as senseless slaughter. Ordering soldiers into a battle to be inevitably mowed down over and over and over is plainly morally abhorrent (as with the Australian and New Zealand Army Corps at Battle of the Nek in Gallipoli during World War I). So perhaps the “reasonable chance of success” condition is best moved to jus in bello (what is just in war). Its existence in jus ad bellum seems—at least from the lessons drawn from a year of (successful) fighting in Ukraine—troubling, if not morally fraught.

Ukraine continues to resist Russian advances, reclaim Russian-held ground, and refuse to concede any territory. According to a Gallup poll, 91 percent of Ukrainians see winning as reclaiming all of Ukraine’s sovereignty. That includes Donetsk, Luhansk, Kherson, and Zaporizhzhya (illegally annexed in September 2022) and Crimea (held by Russia since 2014). With billions in lethal aid pouring into the country, Zelenskyy maintains that Ukrainians “know what [they are] fighting for” and “will never surrender.” Recent reports posit that Putin is ready to deploy 500,000 more conscripts (cannon fodder) to the front line. But, of course, the future of the conflict remains to be seen. Either outcome—victory or loss—comes with costs. Whose bodies pay the price? 

Rhiannon Neilsen is a Postdoctoral Fellow in the Center for International Security and Cooperation at Stanford University. Her research focuses on new technologies in conflict, mass atrocities, dis/misinformation, and the ethics of war. Previously, she was a Postdoctoral Fellow at the Australian National University, a Research Consultant for the Institute for Ethics, Law and Armed Conflict at the University of Oxford, and a Visiting Fellow at the NATO Cooperative Cyber Defence Center of Excellence.

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