(Ця стаття також доступна українською мовою тут. This article is available in Ukrainian here.)

As Russia’s war against Ukraine persists, officials in Ukraine, Russia, and beyond have differing visions of how hostilities should end. Ukraine has consistently made its position clear that no peace negotiations with Russia are possible before the complete restoration of Ukrainian territorial integrity, that is, a return to Ukraine’s 1991 internationally recognized borders. President Volodymyr Zelenskyy laid down that marker when he first outlined his 10-point Peace Formula in November 2022. In contrast, Russia has repeatedly stated that negotiations are only possible with the consideration of so-called “new realities” – that is, Russia’s illegal purported annexation of four Ukrainian southeast regions and Crimea. The two visions would appear to be irreconcilable.

Formally, the majority of the international community expressed their commitment to Ukraine’s territorial integrity with 143 votes at the United Nations General Assembly (UNGA) on Oct. 12, 2022, and through continued support in European regional organizations and recent rounds of high-level talks. In parallel, however, some officials in Western capitals doubt – publicly or privately – that ending the war is possible without Ukraine conceding part of its territory. In mid-August 2023, a senior NATO official, Stian Jenssen, chief of staff to the NATO Secretary General, stated that a potential ending to the war would require Ukraine to give up its territory in exchange for NATO membership, though he later backtracked, saying the statement was a mistake and was only meant to represent one of many “possible future scenarios.”

This was followed by a broader discussion on how Ukraine’s allies envision the end of the war. Journalists report that many Western officials believe that Ukraine’s allies, including the United States, cannot leave it up to Ukraine to define the war’s end goals, since “Ukraine’s maximalist aims, they fear, guarantee an endless war.” These whispering officials, hiding in the diplomatic undergrowth, seem to think that the solution to the conundrum is to offer Ukraine benefits in exchange for accepting a loss of territory and Russia’s plunder of Ukraine’s resources – NATO or EU membership, for example, or military and economic aid guarantees.

Of course, while some “realist” analysts press for such accommodations, none of the diplomats are willing to say this outright. They understand that it is not Ukraine’s “maximalist aims” provoking a possible endless war, but Russia’s undeniable and terrifying imperialistic greed, and they know that such concessions hold not only a potential public outcry but also dangerous ramifications for the global rules-based order constructed so carefully since World War II.

The struggle for peace is not doomed by Ukraine’s legitimate aspiration for restoration of its territorial integrity. These aims and Ukraine’s search for a political resolution, unlike Russia’s hope for territorial concessions, are firmly premised on international law’s constraints – the ones that shape, or should shape, collective security arrangements and the modern world.

Indeed, contemporary international law does not accept anything less than an agreement respecting Ukrainian territorial integrity within its 1991 borders. Any form of territorial concessions in the present environment would be legally void and contrary to duties imposed on States to deny manifest attacks on the international legal regime. Most of all, such concessions would deliver a fatal and final blow to the contemporary world order, while inevitably paving the way to further armed conflict in Ukraine and beyond. It risks being a catalyst for rapacious aggressors who seek to satiate their insatiable appetites on smaller countries and on the international community as a whole.

Illegality of Territorial Bargains Imposed by an Aggressor

Prohibition of the use of force as a means of enforcing, challenging, and destroying the rights of States is the backbone of the contemporary international legal order. Where the law fails to prevent and stop the unlawful use of force, at minimum it ensures that such an illegal act does not produce any legal rights for the benefit of the law-breaker, including acquisition of territorial title as a result of the conquest (Lauterpacht (1953) 233; Lauterpacht’s Report A/CN.4/63 (1953) 148; Schmalenbach (2018) 872). The corollary of this principle is reflected in the law of treaties, which declares void any international agreement procured by the threat or use of force in violation of international law principles enshrined in the United Nations Charter (VCLT, Article 52).

In contrast to the pre-World War I era, when the law permitted war as a legitimate means of dispute resolution and States were bound to recognize unequal treaties imposed by victorious aggressors, further developments culminating in the adoption of the U.N. Charter in 1945 led to an explicit rule invalidating treaties imposed by force. Thus, peace treaties “imposed by the victorious aggressor,” including those legitimizing territorial changes resulting from hostilities, have no legal validity when they are concluded under duress and without consent (Lauterpacht (1953) 233; Lauterpacht’s Report A/CN.4/63 (1953) 147; Schmalenbach (2018) 872).

Apart from guarding the international legal order and State sovereignty, the rule on voidance of imposed treaties is also aimed at guaranteeing stability: treaties imposed under the threat or use of force can further be used as an incentive to later enter into renewed military hostilities to remedy unequal positions (Malawer (1977) 156-157, 165).

Thus, the imposed treaty is absolutely void in its entirety and ab initio (VCLT, Articles 44(5), 69(1)). Its voidance is so fundamental that it is not affected by the fact that a coerced party might obtain advantages from the treaty or its part, or fails to claim the voidance within reasonable time: the coerced party’s acquiescence is irrelevant (Lauterpacht’s Report A/CN.4/63 (1953) 151; see also Rensmann (2018) 867 applicable to VCLT, Article 52 on the basis of Article 45).

Hence, where politics allows for flexibility in discussing potential outcomes of the war, it will eventually have to face the constraints of the law. In the present setting any agreement providing for territorial concessions from the Ukrainian side will inevitably fail the crash test of international law. Be it on its own initiative or under pressure from third States, Ukraine’s territorial concessions will inevitably qualify as consented to only under Russia’s use of force and/or its threat that it will continue to use force or use force in the future if Ukraine doesn’t accept “new [territorial] realities.”

In other words, Ukraine’s consent to its territorial disintegration will remain involuntary for as long as Russian use of force, or its threat, persists to achieve that outcome. As outlined, this conclusion is not any different regardless of whether Ukraine initiates peace talks due to concern about the cost of continuing to defend itself, a shortage of aid or ammunition, or being provided with certain benefits from any imposed treaty (e.g., NATO or EU membership). In all these and like scenarios, the conclusion of a treaty will primarily be the result of the use of force or threat thereof; where the will of Ukraine is effectively reduced “to such a degree of impotence [making it] unable to resist the pressure to become a party to a treaty” (Lauterpacht’s Report A/CN.4/63 (1953) 149).

Accordingly, arguments suggesting that Ukraine’s territorial concessions can bring stability to the world are shortsighted and overlook the legal implications. Any treaty formalizing territorial secession from Ukraine will be a mere ticking time bomb threatening to explode at any time. Since imposed treaties are void entirely and ab initio, the territorial concessions agreement, even if formally consented to by Ukraine, will provide any (current or future) Ukrainian government, irrespective of the passage of time or circumstance, grounds to contest territorial changes. Apart from handing the aggressor ill-gotten gains, and an incentive to resurrect their predatory rapaciousness in the future, this threatens more generally to re-open hostilities at any moment with no real prospect of stability, long-term or otherwise.

International law will not accept anything less than a treaty respecting Ukrainian territorial integrity in its entirety. Allowing otherwise will send the international order back to when aggressive war was legal and territorial conquest was legitimate. It will send a clear signal to (potential) aggressors suggesting that they may attack States that are less mighty militarily or politically, subjugate them, and despite international law prohibitions, enjoy the fruits of their unlawful conquest and the crimes committed along the way.

To prevent this and in furtherance of the prohibition of aggression, international law also imposes several duties on the international community and third States that make the grant of territorial concessions by Ukraine even more untenable. They include the obligations to refrain from any explicit or implicit recognition of a situation created by an act of aggression or rendering aid or assistance to maintain such a situation, as well as the duty to enact measures and/or collective action to bring the violation to an end. As discussed below, these duties are the foundation of the contemporary world order, guaranteeing that the preservation of world peace and security remains a matter of community interest for all States, without leaving the victim of aggression facing its consequences alone.

Obligations Incumbent on the International Community and Individual States

The prohibition of unlawful use of force is widely regarded as a peremptory norm of international law (jus cogens), i.e., an international law rule from which no derogation is permitted (ARSIWA 112, §4; International Court of Justice (ICJ) Nicaragua (1986), §190). Various legal consequences are considered to follow from serious breaches of obligations arising under a peremptory norm such as that of  Russia’s aggression and subsequent occupation/purported annexation of Ukrainian territory (ARSIWA, Art. 41), including those relevant to proposed territorial concessions or any other grubby bargaining with Ukrainian land.

The various duties and obligations below are applicable to all the constitutive elements of Russia’s exercise of jurisdiction. This is not solely limited to legislative and administrative acts that purport to revise the international legal status of the territory, but also it concerns the rights, entitlements, and benefits of public and private entities contributing to or benefiting from the unlawful exercise of jurisdiction by the de facto authorities (Azarova (2018) 53-54). As jus cogens norms protect the common interests of all States, it must be expected that all will invoke the illegality of their breach and work to expel them from international life (Orakhelashvili (2003) 3).

Duty of Non-Recognition

Incumbent on third-party States is a duty of non-recognition towards the lawfulness of a situation created by a serious breach, e.g., the act of aggression (ARSIWA, Art. 41(2)). Its customary nature is well-established through international practice and ICJ decisions, which implies that it exists independent of treaty law and is binding on all States (see UNGA Declaration on Friendly Relations A/RES/2625 (1970); UNGA Declaration on the Definition of Aggression A/RES/3314 (1974); ICJ Nicaragua, §188; ICJ Wall, §159).

Arguably, the duty of non-recognition forms the minimum necessary response by States to such serious breaches (ARSIWA 115, §8). This principle itself was first developed in relation to acquisitions of territory by force (Aust (2011) 330), and was further crystallized in the U.N. General Assembly’s 1970 Declaration on Friendly Relations, which expressly refers to the non-recognition of territorial acquisition resulting from a use of force in breach of the U.N. Charter. It essentially holds that, regardless of how long the fruits of aggression endure, the aggressor should never benefit from its wrongful acts, including by legitimizing territorial changes.

This duty may be argued to be self-executory in that, for it to be triggered, States do not necessarily require a pronouncement of illegality of the situation by an impartial and authoritative body. This is notably seen in ICJ Wall Advisory Opinion (§154-159), where the Court does not seem to root the existence of the duty and corollary obligations in a pre-existing U.N. resolution (unlike in ICJ Namibia, §115-119).

The ICJ has generally erred on the side of expansive non-recognition in circumstances involving unlawful acquisition of territory through use of force (see ICJ Wall and Namibia). Although ideally the measures practically entailed by this duty “should” be specified by the appropriate political organs of the United Nations acting within their authority under the Charter, the absence of such direct directives is not fatal to the duty’s applicability. While the ICJ had arguably initially implied such a view (ICJ Namibia, §120ss); a more recent position seems to sustain the duty’s enduring application in the absence of such official dictates (see ICJ Wall, §159). This is especially so in considering that state practice has moved in this direction and that the U.N. General Assembly and the U.N. Security Council have primarily political – not judicial – mandates (as the State representatives within typically seek to enact political agendas as diplomats, not jurists) (Costelloe (2017) 203-204).

Acts that amount to recognition, and must thus be avoided, may consist of explicit or implicit conduct (ARSIWA 114, §5). Though a mere declaration not to recognize a claim to a given title is certainly a minimal requirement, more exacting measures of isolation have been employed where their pursuit would permit the unlawful exercise of authority to become further entrenched. Examples of such measures include abstaining from entering into treaty relations, suspending diplomatic relations, and ceasing economic cooperation. (Aust (2011) 330, 333; Lauterpacht (1947) 431ss; ICJ Namibia, §121-124).

These are all tools to address acts taken by a State related to annexed territory. The goal is to prevent a State from consolidating the effects of that breach and the gains that such a breach can potentially produce. Consistent with this, States must ensure that their dealings with an annexing State do not extend to the foreign territory it seeks to illegally annex (Azarova (2018) 54).

These principles are particularly relevant in light of clandestine discussions on territorial concessions and associated bargains. Given the incontrovertible evidence of flagrant Russian aggression and the self-executory character of the duty of non-recognition, such non-recognition is triggered irrespectively of whether any pronouncement has been made by an international body. In any case, the U.N. General Assembly has consistently recognized Russian occupation of Ukrainian territories since 2014 as “violations” of Ukrainian territorial integrity and “aggression” (UNGA A/RES/68/262 (2014); UNGA A/RES/ES-11/1 (2022)), which guarantees that the duty of non-recognition has been triggered.

This entails various legal consequences for third States, including most importantly, the duty not to recognize any Ukrainian territorial concessions, e.g., either through explicit recognition of a peace treaty that normalizes such Russian claims, or implicit acceptance (e.g., through economic and financial cooperation with occupied territories).

Prohibition of Rendering Aid or Assistance

A corollary obligation under customary international law is the prohibition of rendering “aid or assistance” to the responsible State in maintaining the situation created by the breach of a peremptory norm (ARSIWA, Art. 41(2); ICJ Wall, §159). While it overlaps with the duty of non-recognition, it extends beyond that, as it aims to prevent acts that would not necessarily imply recognition but provide a “significant contribution” to the unlawful situation (ARSIWA 115, §11-12; Aust (2011) 340-341).

What amounts to such aid or assistance will depend on the context, from providing military support to simply financing the wrongdoing state (Costelloe (2017) 207). Although the prohibition tackles more concrete measures impacting directly upon the wrongful situation, it may also arguably encompass political forms of support overlapping with the duty of non-recognition (Aust (2011) 337).

Based on this, it is apparent that States providing military or material assistance in furtherance of Russian aggression against Ukraine and related international crimes (such as in the cases of Iran or potentially North Korea) are in violation of the duty of non-assistance. However, in the same vein, it may be reasonable to consider that States providing enduring political support to Russian war goals (e.g., Belarus – see here and here) should be no less responsible for aiding and assisting the act of aggression than those whose support is more tangible.

This provokes several questions. For example, does voting in international venues against resolutions in support of Ukrainian territorial integrity in response to Russia’s illegal annexations (e.g., Belarus, North Korea, Nicaragua, and Syria) amount to the act of aiding and assisting? In a way, it might constitute a direct and significant contribution to these territorial acquisitions by force by impeding the non-recognition of the unlawful situation or measures prompting its end, as well as ensuring that the effects of the violation can be more easily consolidated.

The same will be true in the reverse scenario. In a hypothetical case, where Russia tries to formalize its territorial gains by initiating action in international venues, voting in favor of such action may present a case of aiding and assisting the breach by ensuring that its fruits persevere. In another hypothetical scenario, third States prescribing territorial concessions as the sole acceptable outcome of peace talks and making clear efforts to push the victim of aggression to concede may run afoul of their duty of non-assistance under international law.

Finally, the duty of non-assistance raises many other potential dimensions currently unexplored in the context of aggression, such as the connection between imposing/maintaining countermeasures and compliance with the duty of non-assistance. For example, where countermeasures were imposed in order to induce an aggressor to terminate their use of force, can the weakening or lifting of such sanctions – in certain circumstances – be regarded as a form of aiding and assisting? Although it may seem atypical in comparison with more widely cited forms of assistance, it might arguably significantly facilitate and encourage the aggressor to further the act of aggression by breaking the existing and deterring status quo, while paving the way for territorial acquisitions and allowing the aggressor to rebuild, colonize, and consolidate its grip. The article will leave this issue aside for more extensive future debate.

Duty of Positive Measures/Collective Action

Finally, the most exacting norm that may arise from a serious breach is an obligation to cooperate to bring it to an end through lawful means (ARSIWA, Art. 41(1)). In contrast to the duties outlined above, this obligation does not merely require States’ relatively passive abstention from facilitating the unlawful annexation, but likewise to undertake proactive actions to bring an end to the violation.

The standing of such a duty as a customary principle still seems subject to debate (ILC Report A/77/10 (2022) 71, §3; Aust (2021) 245). However, in contexts of aggression, there are clear obligations of States to cooperate with each other “in order to maintain international peace and security,” as cited in the U.N. General Assembly’s 1970 Declaration on Friendly Relations. That might arguably take the form of undertaking collective action aimed at restoring the territorial integrity breached as a result of the unlawful use of force.

Where the violation of a peremptory norm has been recognized by the U.N. Security Council or the General Assembly, the ICJ has recognized a binding obligation on States to make efforts to bring resulting situations to an end via collective action (ICJ Namibia, §86, 121-124; Wall, §21, 159-160). In the current context, the occupation of various Ukrainian territories since 2014 as a direct result of Russian aggression has been deemed invalid and considered a “violation” of the UN Charter by multiple UNGA resolutions (inter alia, UNGA A/RES/68/262 (2014); UNGA A/RES/ES-11/1 (2022)).

While such collective action could (and perhaps ideally should) be organized through international organizations such as the U.N., it need not be limited to institutionalized forms of cooperation (ARSIWA 114, §2). This is particularly relevant to situations flowing from the actions of permanent members of the U.N. Security Council, such as Russia in this case, who wield the ability to paralyze coercive organizational measures. Beyond the collective framework, the ICJ has appeared to hold that this obligation may make it incumbent on States to individually take measures to bring situations created by the breach to an end (ICJ Wall, §159).

No specific acts or thresholds can be objectively required of cooperative (or individual) measures, given the diversity of circumstances involved and realities facing third-party States. Yet what this duty may encompass could be inspired by the proactive measures of the Economic Community of West African States (ECOWAS) in response to repeated coups d’états in the region. This involves actions such as economic sanctions, exerting diplomatic pressure (from public criticism to red lines in negotiations), and travel bans for certain individuals.

Hence, in addition to negative duties to abstain from legitimizing or facilitating annexation, international law also seemingly requires States to act proactively to bring an end to the violation. On the face of it, upholding the existing pressure on Russia with countermeasures and continuing political, financial, and material support to Ukraine seemingly represent a minimum of acts sufficient to meet the duty of positive action. The pressure and support thus should persist for as long as the violation continues.

Moreover, as is also now crystal clear, if Ukraine is forced into territorial concessions, the price to be paid is not solely in land but also in the millions of people exposed to Russia’s atrocities and national and political persecution (see, e.g., UNCOI (2023), OHCHR (2023), HRW (2022)). With the same impetus that is felt by Ukraine and its soldiers on the frontlines for liberty and freedom, the international community has an onerous and incontrovertible duty to fight for Ukraine’s sovereignty and territorial integrity. A calamitous reversal of Ukraine’s struggle based upon ambivalence is not an option available in international law.


International law architecture, including the prohibition of the use of force, was not imposed by some abstract legislature or idealist. It emanated from human civilization’s common will and vision of elevated principles that evoke a future free of violence and that mark humankind’s progress as a whole. The law might not have arms to immediately terminate or suppress aggression and the atrocities accompanying such a violation, yet the law at least refuses to reward the aggressor for persevering with its illegitimate acts. Faced with the eventual resolution of the current war in Ukraine, the scarcity of inter-State armed conflicts being concluded by treaty in the post-WWII era lends particular weight to such a salient international collective response.

The obligations and duties discussed form many sides of the same fundamental prism: the solidarity of the international community in the face of serious attacks against the rules which protect the fundamental values collectively adopted. Where the violations occur, it is the basic function of the law, as a primary social regulator, to ensure that the fruits of the violation will, at minimum, not endure or withstand historical examination. Ultimately, those responsible shall face accountability in courts of law. Anything less will weaken the world order, as well as the law that is essential for its maintenance, development, and prosperity.

Hence, there is no alternative to Ukraine reestablishing its territorial integrity in its entirety. This is the only way not only to reaffirm shared values but – even more pragmatically – to secure the world from even greater chaos and endless war that would flow from permitting or facilitating Russia’s territorial acquisitions. Most essentially, it is the only way that millions of people in occupied territories can be protected from displacement, persecution, and Russia’s destructive bent. The Ukrainian allies’ proud narrative of supporting Ukraine “for as long as it takes” should not remain merely a matter of being “on the right side of history” but – primarily – the manifestation of a sacred legal duty. This is the choice of – and for – the future: the choice between the rule of law and the reign of chaos.

IMAGE: Ukrainian servicemen of the 65th Mechanized Brigade walk near the frontline village of Robotyne, in the Zaporizhzhia region, on October 1, 2023, amid the Russian invasion of Ukraine. (Photo by ROMAN PILIPEY/AFP via Getty Images)