(Ця стаття також доступна українською мовою тут.)

The recent aggression against Ukraine and the lack of a collective military response are seen by some as demonstrating the failure of the global legal order. The concerns about such failure invite a reassessment of the tools that international law offers for preventing wars or hastening their peaceful termination. In this essay, we briefly examine these tools and argue that they go beyond the direct prohibition on the threat or use of force and the collective security mechanism of the United Nations (U.N.) Security Council. We begin with the insight that has informed conflict theorists such as Carl von Clausewitz and Thomas Schelling, namely, that war is a continuation of bargaining process that failed to achieve a more peaceful solution. We propose that the real thrust of a variety of norms of international law is to render the military option less attractive than the peaceful one.

Why Do Nations Go to War?

To assess the role of law in preventing wars, we must first ask why it is that nations use force in the first place. Relying in part on previous scholarship, we propose that the turn to violence could reflect five distinct problems: indivisible goals, information asymmetries, commitment problems, externalities on third parties, or agency costs. The war in Ukraine manifests all these problems:

(a) Indivisible goals: Total wars, or wars aiming at the complete subjugation of the opponent and terminating its existence as a political entity, are conflicts to which there can be no peaceful agreement. When Russia denied Ukraine’s right to exist as an independent nation or demanded regime change, there was little to negotiate about peacefully.

(b) Information Asymmetries: Rivals may fail to realize the fighting power of their opponent and its determination to fight. Rivals have an incentive to cheat their opponent, either by overstating their power and commitment or by understating their true capabilities. As Schelling noted, rivals always seek to “keep the enemy guessing.” Apparently, Russia’s intelligence failed to grasp the full magnitude of Ukraine’s capacity and resilience.

(c) Externalities on third-parties: In the past, fighting between rivals affected their respective resources. War was seen, in Clausewitz’s words, as a duel between two nations: “War is nothing but a duel on a larger scale [between] a pair of wrestlers. Each tries through physical force to compel the other to do his will.” In the past, it was primarily the warring parties which suffered the economic consequences of war. The globalized economy has changed this dynamic. Today, disruptions in distribution of key products such as oil, wheat, or diamonds can actually benefit an aggressor with soaring prices of commodities that can help it finance the war and occupation. No doubt, planning for conquering Ukraine took into account the global dependence on Russia’s oil and gas, and on Ukraine’s wheat and neon gas, to help fund the war and to obtain the world’s acquiescence for the fait accompli.

(d) Commitment problems: Bargains in the form of peace agreements, for example, will be avoided if they cannot be sustained or enforced in the long term. The Budapest memorandum, in which Russia, the United States, and the United Kingdom recognized Ukraine’s borders, and the Minsk Agreements in which the parties agreed on a ceasefire in the Donbas region of Ukraine, to be monitored by the OSCE, were proven to be ineffective at containing Russian aggression. NATO’s unwillingness to intervene in the current crisis outline the limits of any future collective guarantee for Ukraine’s future.

(e) Agency costs: Leaders may be tempted to resort to military force to boost their popularity at home, or due to faulty information provided by subordinates seeking to please their leader. Once war starts, leaders may choose to continue with it despite strategic losses due to concerns about their ability to hold on to power after conceding defeat. As H.E. Goemans observed, “If the consequences of the terms of settlement appear particularly nasty for political leaders—if they can personally expect severe punishment as a result of these terms—leaders can rationally prefer to continue fighting as long as there is a chance they can get terms that prevent their punishment.” While he further suggested that “semirepressive, moderately exclusionary regimes” are particularly prone to select this option, gambling for resurrection could be a rational choice for tyrants and democratic leaders alike. Authoritarian leaders are prone to be misled by subordinates. Recent reports indicate that Putin realized that a unit of Russia’s FSB was “afraid to anger the leader [and] simply supplied him with what he himself wanted to hear” about the situation in Ukraine. An internal power struggle in Russia to remove Putin is not impossible, and it highlights Putin’s dilemma: while it is beneficial for Russia to end the war as soon as possible, for Putin himself such an outcome could prove disastrous in terms of his own political power.

How Does International Law Address These Bargaining Failures?

International law has sought to address each of these five bargaining failures through several doctrines. While we tend to focus only on the prohibition on aggression, or the role of the U.N. Security Council, international law offers other, less direct but perhaps even more effective, legal rules that impose significant obstacles to pursuing the military option. While these obstacles may ultimately prove insufficient to prevent wars such as the current conflict in Ukraine, their very existence demonstrates the potential to address the root causes of war outlined below:

(a) Indivisible goals: International law precludes the pursuit of certain aims, removing them from the bargaining table. Conquest and annexation are unequivocally contrary to the principle of territorial integrity of sovereign states, and regime change similarly runs afoul of the principle of national self-determination and political independence. Such aims are violations of jus cogens (the most paramount international law), have no legal validity and may not be recognized by third parties (Article 41 of Articles on State Responsibility). These principles were first asserted by the Stimson Doctrine (1932) which was regarded, already by the League of Nations, as reflecting the law. Putin’s demand to subjugate Ukraine was not a legitimate bargaining demand. This is the first legal obstacle that he violated.

(b) Information Asymmetries: While it is obvious that aggression itself is prohibited, it is less clear why the threat to use force is also prohibited and constitutes a violation of the Charter as such. We propose that the reason behind the prohibition to issue threats, as well as the expectation that all parties explain their decision to use force, reflect an effort to reduce information asymmetries. By the mere issuing of a threat or by the assertion of fabricated justifications for resorting to war, leaders signal their resolve to attack. In other words, international law adds credibility to the speaker’s message: If they already violate the prohibition to threaten war, there is a high risk they will act upon this threat. When Putin asserted contrived reasons to justify his order to invade Ukraine he issued a credible threat that put the Ukrainians on notice of a pending imminent attack. The threat was a violation of the law in and of itself; the legal Rubicon had already been crossed.

(c) Internalizing externalities: In the past, as fighting remained a duel between two nations, third parties were expected to remain neutral. The laws on neutrality were highly developed and secured a bargain between the neutrals and warring parties; neutrals committed not to intervene militarily or economically in the ongoing conflict. During World War II a more nuanced distinction emerged, allowing neutral parties to take sides without violating neutral obligations or becoming directly involved in the war. According to this view, neutral states are allowed to adopt a position of “qualified” or “benevolent” neutrality, distinguishing between an aggressor against which they might act, and the victim of aggression to which they could offer support.

We propose that this development in the law on neutrality, as also reflected in a parallel development in the law on state responsibility, reflects an increasing inter-connected global economy which transforms bilateral conflicts into global ones. International law responds by recognizing that an act of aggression can be regarded as perpetrated not only against the victim state but also against “the international community as a whole” (Article 42(b) of Articles on State Responsibility), and third states have a right to respond to such aggression and an obligation to “cooperate to bring to an end” this serious breach (Article 41(1) of Articles on State Responsibility).

As a result, the party contemplating recourse to force must take into account the coercive reactions not only of the victim state but also of third parties. As “collective victims” of aggression, third parties may, just like the initial victim state, take countermeasures, including by not performing international obligations owed to the responsible state. The old laws of neutrality have lapsed.

Obviously, it will often be contentious to assess whether qualified neutrality or a collective injury are valid claims. Here again a tool has been created to provide international guidance: the 1950 Uniting for Peace Resolution of the U.N. General Assembly affirms that if two-thirds of U.N. members believe that an act of aggression has taken place, and the Security Council is not responding to it, then the General Assembly may recommend measures for states to take collectively in response to aggression. Such a Resolution was adopted days after the invasion of Ukraine, helping to solidify the basis for countermeasures against Russia.

(d) Resolving commitment problems: The “law on peace” provides some tools to make agreements stickier, for example, by using third states as guarantors, or demanding popular endorsement of major political changes through referenda. An example of the first option is the establishment of U.N. bodies’ monitoring agreements. But these legal tools are lacking in the exceptional case of Russia, a power that has the capacity to resort to nuclear warfare and wields a veto in the Security Council.

(e) Agency costs: International law provides face-saving solutions to leaders wary about the potential political fallout of making concessions. A request for a parliamentary approval of a military response, a recourse to the U.N. Security Council before war begins, or to arbitration before or during war are tools for leaders to eschew agency by relegating the responsibility for accepting concessions on others without signalling weakness or lack of resolve. But international law can also exacerbate agency costs with its criminalization of aggression, since it might incentivize leaders who are wary of being prosecuted for war crimes to continue fighting rather than capitulate (but at the same time this might incentivize other war criminals, hoping to gain clemency, to rebel against their leader)). The ability of the Security Council to suspend such investigations or prosecutions may, as David Bosco explains, come in handy down the line. If such suspension is conditional on the state’s continuing compliance, the commitment problem might also be resolved, at least as long as the criminals continue to lead the aggressive state.


Understanding the factors that can derail peaceful bargaining, and observing their role in the Russian-Ukraine War, is important for understanding the potential utility and limits of international law. In a 2016 study, The Puzzle of Peace: The Evolution of Peace in the International System, Gary Goertz, Paul F. Diehl, and Alexandru Balas  show that “rivalry has declined and peace has increased since World War II,” suggesting that this was a result of “the development of a strong set of international norms supporting territorial integrity and mechanisms that manage territorial conflicts when they occur.” We argue, instead, that it is not that peace was the unintended indirect consequence of background norms such as territorial integrity, but that those norms, even more than the explicit norm that prohibits aggression, were designed to prevent wars. From the Stimson Doctrine onwards, the real thrust of a variety of norms of international law was to render the military option less attractive than the peaceful one. Granted, the direct prohibition on aggression was a crucial element in this endeavour. But the latter almost immediately proved to be ineffective, as demonstrated by Adolf Hitler’s false invocation of the self-defense exception clause during World War II. The main thrust of international law instead has been to raise the costs of war in inter-state bargaining: limiting indivisible goals in conflicts, making private information public, limiting externalities on third parties, enhancing commitment to agreed outcomes, and resolving agency problems within states.

We propose that international law offers a much wider and elaborate set of tools to prod adversaries to rationally avoid the military avenue for resolving their disputes. The Russian aggression represents a case in which all the five factors drove heavily toward the military option: Russia’s aims seemingly were not negotiable; it had poor information about the capacity and determination of Ukraine’s military and citizenry; it hoped to externalize the costs on the rest of the world; its commitments had no real value; and its leader’s personal interests diverged from those of the state. Against such a rare and deadly constellation, what international law has to offer is fairly minimal, but even if it is not immediately effective, it is evolving toward tackling even the hardest cases.

Image: Silhouette of soldiers on Ukrainian and Russian flags (via Getty Images).