Revue Européenne du Droit
International Law and War in Light of the Ukrainian Conflict: A Relation Biased Since Its Inception
Issue #5


Issue #5


Jean-Marc Sorel

Legal Journal published by the Groupe d’études géopolitiques in partnership with Le Club des juristes

Jus ad bellum and jus in bello. Traditionally, a distinction is made in international law between the jus ad bellum, the right to wage war or the right of a state to resort to war in a lawful manner, and the jus in bello, the law governing the conduct of war, which includes international humanitarian law, the law of neutrality, but also today international criminal law. The jus ad bellum is derived from the old customary basis of international law and has been progressively limited since the end of the 19th century, before the Charter of the United Nations prohibited the use of force between states. But the engravement of limits to the right to wage war in what seemed to be the marble of international conventions during the Peace Conferences in The Hague between 1899 and 1907 left many skeptical back then already. The irruption of the First World War shortly afterwards gave a sad illustration. The jus in bello is today on everyone’s mind, as a result of the de-structuring of wars, most of which are the result of internal and not international conflicts. 

The aggression of Ukraine by Russia is nevertheless a masterful exception to this pattern, which almost seemed to have put inter-state wars in the storehouse of antiquities. It is easy to understand, however, that these distinctions are often reduced to a simple reality, that of the hypocrisy of the use of force, most often outside the prescribed rules, with countless violations of humanitarian law. In this respect, Article 51 of the United Nations Charter on the ‘inherent right of self-defense’ has been the main pretext for the use of force since the Second World War, forgetting, on the one hand, that this power is conditioned ‘until the Security Council has taken the necessary measures’ and, on the other hand, that it is not subject to interpretations (such as ‘pre-emptive’ or ‘preventive’ self-defense) which extend it ad infinitum.

The right to [wage] war: indifference to the cause as long as it seems just. In the end, states never managed to get rid of the idea that they were waging a just war, which gave them the ‘right’ to do so. This is of course the position that the Russian Federation wishes to adopt, placing the idea of a just war above all imperative norms, chief amongst them the prohibition of wars of aggression. 

This ‘feeling’ has a long history. In the dispute between Sepulveda and Las Casas, the central question was indeed that of the right to wage war, through its moral formulation, ie the question of the just war. This is apparent from the title of Sepulveda’s work—On the Just Causes of War—which sets the tone. 1 Las Casas received the support of Francisco de Vitoria, an illustrious theologian who rejected the very idea of a just war. But reflections on the connection between war and justice were not, however, new to the 16th century. 

Believing that a war can be just is a dead end, since justice and injustice are not real but relative qualities. This furrow will nevertheless be dug for centuries, through multiple projects promoting the idea that perpetual peace can protect against wars because the latter can never be ‘just’. These ‘peace through law’ projects  assumed that law had this power, when it is only the reflection of a power relationship at a given moment. Many tried (Sully or the Abbé de Saint-Pierre in particular), but the most successful project remains that of Kant in Toward Perpetual Peace: A Philosophical Sketch: ‘The state of nature (status naturalis) is not a state of peace among human beings who live next to one another but a state of war (…) [h]ence the state of peace must be established.’ 2

It is thus necessary to legally ‘establish’ a state of peace in order to prohibit a ‘natural’ war. This is a strange philosophical conception which is probably more rooted in historical observation than in reflection on the nature of humankind, or else it is necessary to ‘establish’ (that is to say ‘educate’) human beings rather than to think about natural violence. Nevertheless, the result is that peace is considered in opposition to war, as a simple interlude between two wars, as hope during a conflict, or as an unattainable ideal, all of which are intertwined. Peace sometimes seems more difficult to apprehend and to live than war. This ranges from the most absolute pessimism to a sometimes-blissful optimism. The pessimistic vision is that of a peace that always hides a future war, violence being natural and legitimate, and that it can be just. In Ukraine too, there were already hidden wars preparing the present one. There was no peace before the interstate war of 2022, but latent wars as a prelude to the open war. 

The war before the war. Since the independence of Kosovo, lived as a setback by the leaders of the Russian Federation, all the actions taken by the latter tend to prove that, on this basis, all kinds of secessions and annexations are possible insofar as a Russian-speaking population feels aggrieved: Georgia with the self-proclaimed republics of Ossetia and Abkhazia in 2008, before that Transnistria in Republic of Moldova, and of course Crimea in 2014, and then Donbass. Consider the ‘Minsk Agreements’ of September 2014, negotiated under the aegis of representatives of the Trilateral Contact Group on Ukraine (Russia, Ukraine and the OSCE) to achieve a peaceful settlement of the conflict in Donbass. The agreements failed almost immediately. None of their provisions were fully implemented, including the ceasefire that was at their heart. Indeed, President Putin has cited their failure as one of the reasons for invading Ukraine. In any case, Ukraine was already at war with the Russian-aided ‘separatists’ since 2014. 

And this war was not only on the ground, but also before the courts. Whether before the International Court of Justice (Application of the International Convention for the Suppression of the Financing of Terrorism and of the International Convention on the Elimination of All Forms of Racial Discrimination (Ukraine v. Russian Federation)), via arbitrations (Dispute Concerning Coastal State Rights in the Black Sea, Sea of Azov, and Kerch Strait (Ukraine v. the Russian Federation) before the Permanent Court of Arbitration) including in investment matters (seven cases between 2017 and 2019), before the International Tribunal for the Law of the Sea (Dispute Concerning the Detention of Ukrainian Naval Vessels and Servicemen (Ukraine v. the Russian Federation)), or finally before the WTO (Measures concerning traffic in transit, Measures affecting the import of railway equipment and their parts). 

Russian legal pretexts for war, the continuation of the deviation from jus ad bellum. Recall and legal arguments and facts of the Russian Federation’s aggression. On February 21, 2022, the President of Russia signed a decree by which two secessionist territories in eastern Ukraine were recognized as independent states, namely the Donetsk People’s Republic and the Luhansk People’s Republic. On February 22, 2022, treaties of friendship and mutual assistance between the Russian Federation and each of these ‘states’ were ratified by the Federation Council (the upper house of the State Duma). On February 24, 2022, Russia launched a military operation against Ukraine, with Russian armed forces entering Ukrainian territory. 

The legal arguments are essentially contained in Vladimir Putin’s televised address of February 24, 2022: first, preventive self-defense, faced with the threat of NATO enlargement and the alleged desire of the ‘totalitarian’ regime in Kiev to acquire nuclear weapons and prepare an attack against the Russian Federation, requiring in particular an effort of ‘denazification’ and demilitarization of Ukraine; second, the alleged genocide committed by Ukraine in the separatist territories, the Russian military action being aimed at putting an end to it; finally, the request for assistance presented by the two ‘states’ recognized by Russia, by virtue of the right to collective self-defense provided for in Article 51 of the UN Charter and on the basis of treaties of friendship and mutual assistance. 3  

This is a summary of all the pretexts accumulated in contemporary history for unjustified military interventions, be it the former French military actions in Africa, the justification for the 1979 intervention in Afghanistan by the Soviet Union, or the more recent intervention by the United States and its allies in Iraq in 2003. Jurists may be satisfied with the legal arguments invoked for each one of these actions, which means that the aggressor state feels obliged to wrap its actions in a legal justification; but satisfaction ends there, because legal arguments are just a smoke screen. Add to that the masquerade of the sham referendums after which four regions of Ukraine (Lugansk, Donetsk, Zaporizhzhia and Kherson) officially joined the Russian Federation on 30 September 2022.

What are we left with? A war that cannot be halted, but whose excesses one can still hope to mitigate. 

Jus in bello: repression in the absence of prevention. Absent realistic means to limit the war, the conflict in Ukraine illustrates the much-publicized reliance on the jus in bello. Paradoxically, this attests both to an undeniable progress and a tragic renunciation. Peacekeeping in its UN version being, to say the least, jammed (if not definitively discredited), the question is no longer that of halting the war, since this is impossible, but that of mitigating its consequences and planning for a post-war period, whenever it may come. For this purpose, we multiply conferences with future donors (or investors), we deal with humanitarian tragedies as best as we can, and we brandish justice against the impunity of aggressors. Punishing the aggressor would be a progress (provided we manage to do so), but preventing the aggression would be even better. The renunciation is here: if we cannot stop the aggressors in their actions, we hope to punish those responsible. This is not so simple, since the aggressor often claims to respect the law, and the aggressed is not exempt from responsibility in certain exactions, the reciprocal accusations too often resembling schoolboy quarrels. The flagrant violations of jus in bello by the Nazi regime did not prevent it from having a War Crimes Office, dependent on the legal department of the Wehrmacht, composed of jurists. This example is not isolated. What is striking is the impeccable legal and hierarchical order that seems inversely proportional to the respect of the rules applicable to the conduct of wars. 

Courts are opening up again, but the legal battle is no longer pseudo-economic, but rather on the defense of humanitarian law. In addition to a new referral to the International Court of Justice by Ukraine to show that it is a victim of genocide, and deny the Russian Federation the argument that it is a perpetrator of genocide, the International Criminal Court (‘ICC’) started investigations into various crimes, on the basis of a cooperation with Ukraine and the support of many ICC member states. This procedural magic thus allows ICC to rule on crimes against humanity, war crimes and genocide, but it does not allow it to rule on the crime of aggression, an eternal sea serpent that blocked legal progress for a long time before the General Assembly agreed in 1974 on a definition that is still used today. Indeed, the Court can only exercise its jurisdiction over the crime of aggression when it is committed by a State Party to the Rome Statute, and if the State Party has ratified the relevant amendments. Ukraine is not a party to the Rome Statute. Hence the resurgence of the idea of an ad hoc jurisdiction that could compensate for this inability. 4  

The machinery would be complex and the outcome uncertain but, in addition to the many humanitarian actions undertaken by numerous actors (intergovernmental organizations, NGOs, states, etc.) whose benefits cannot be denied, there remains a central question (which is not new): how to reconcile the necessary condemnation of those responsible with the search for the truth, which goes far beyond this framework because it implies a much broader form of transitional justice more capable of getting to the roots of the evil. 5 Rendering justice is an element of peace but it is not peace. It is one element among others of transitional justice. One can think in particular of the Russian population (of Russia or elsewhere) raised in the belief of a form of resurrection of the tsarist power, and it is above all to this population that one must address oneself in order to enable it to have a critical view of its President-dictator. And this is the most important thing. Judging Putin and his acolytes is of course important, but it is also necessary to avoid making him a martyr and a victim of the victors’ justice in the eyes of his population. Mladić is on trial, but huge portraits of the deposed general still adorn the streets of the towns of the Bosnian Serb Republic, with the inscription: ‘Come back, we’re waiting for you.’

As it stands, the jus in bello can create barriers but cannot resolve the issue, dependent as it is to jus ad bellum, whose roots stretch back to the origin of violence between entities (not yet states), but whose legal restrictions have never succeeded in dissuading states that have the means to do so from waging what they consider to be a just war, without fearing ridicule most of the time.

If jus ad bellum and jus in bello are surprising, it is not because of tragic aspects which, conversely, should frighten, but because frightful events are not halted by these ‘laws’, a tragedy that can only raise eyebrows considering the great distance that separates the norms and their application.  This is not a reason to give up on the law, but one should be keenly aware of its role and its effectiveness, which are circumscribed to good-faith actors willing to subject themselves to it. Unfortunately, while bad faith is sometimes apparent in the actions of certain states, it remains the most difficult thing to prove, and not only legally.


  1. Juan Ginés De Sepulveda, ‘Democrates Alter, Or, on the Just Causes for War Against the Indians’, in Columbia College (ed.), Introduction to Contemporary Civilization in the West (Columbia University Press 1946).
  2. Immanuel Kant, Toward Perpetual Peace and Other Writings on Politics, Peace, and History (Yale University Press 2006), 72-73.
  3. On the use of the principle of self-determination, see in this volume the contribution of Pietro Pustorino.
  4. See the contribution in this volume by Federica D’Alessandra
  5. See the contribution in this volume by Elisenda Calvet-Martínez and Elena Baylis.
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Jean-Marc Sorel, International Law and War in Light of the Ukrainian Conflict: A Relation Biased Since Its Inception, Jun 2023,

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