The Jus ad Bellum Aspects of the Russian War in Ukraine


| Jan 29, 2024


Editors’ Note: This post is derived from a presentation given at the 2023 Israel Defense Forces Military Advocate General’s 4th International Conference on the Law of Armed Conflict.

In spite of the complex legal issues that Russia’s full-scale war in Ukraine has raised for States that seek to bring to an end this flagrant violation of international law, its jus ad bellum aspects seem fairly straightforward. There is no need to assess different interpretations of the right of self-defence, intricate arguments related to the availability of a UN Security Council resolution, or the consent of the territorial State. Unlike a number of earlier uses of force of doubtful legality, this is a textbook case of an act of aggression. While the legal characterization of the “special military operation,” as Russia calls it, is not likely to raise questions, there is reason to reflect on its broader implications. In particular, how could such action by a permanent member of the Security Council affect the Charter-based regime on collective security, including the integrity and power of the general prohibition of the use of force?

In this regard, it should be recalled that the prohibition on the use of force has proved resilient in the past, including in the face of deliberate efforts to change its established interpretation. This was the case, for instance, with the discussion on humanitarian intervention after the 1999 Kosovo War and the pre-emptive self-defence argument presented in the National Security Strategy of the United States under the George W. Bush administration. Neither effort proved fruitful, and the UN World Summit of 2005 concluded that the UN Charter’s provisions on the use of force offered a sufficient basis for addressing all potential threats to international security.

Reaffirming the Jus ad Bellum Framework

As a general matter, violations of a rule do not change the rule. This is true at the national level as well, whether the question is of traffic rules or criminal law. The process of changing international law is much more complex, even more so in the case of a peremptory norm of general international law, which can only be replaced by a rule of a similar status. The implications of a gross violation of international law depend, first, on how other States react to the violation.

In the present case, a clear majority of more than two-thirds of the UN membership (141 States) condemned the Russian invasion of Ukraine as an act of aggression, demanding that the Russian Federation unconditionally withdraw all its forces from Ukraine. Only a handful of States voted against the resolution. Such a clear condemnation strengthens the general prohibition on the use of force against the territorial integrity or political independence of another State.

Furthermore, the many current initiatives concerning the establishment of a court of aggression, or a compensation mechanism, and collection and preservation of evidence to deal with the international responsibility of the Russian Federation and Russian leaders, are also testimony to the continued perception of the prohibition of the use of force as a powerful constraint on State action. So also does Ukraine’s determined defence of its territorial integrity and political independence.

Second, as the International Court of Justice has pointed out, one-off violations of an international legal rule do not threaten its existence when the violating State frames its action within recognised exceptions to that rule. Even implausible justifications reaffirm the existing rule and prove that the State does not seek to introduce an alternative. In such cases, the disagreement is about facts rather than the state of law. The legal justifications Russia has presented in support of its armed action in Ukraine, few as they are, largely build on the right of self-defence. This is clear from President Putin’s television address of 24 February 2022, in which he explicitly stated that Russia was acting to defend itself, adding that the action was “in accordance with Article 51 (Chapter VII) of the UN Charter.” Even more importantly, Russia complied with the reporting requirement of Article 51 and sent a letter to the Security Council, with President Putin’s speech as an attachment. While Russia has acted in gross violation of the UN Charter, it has thus not questioned the content or the binding nature of the rules of the Charter.

The Question of Imminency

A question has also been raised concerning the moment, before the actual attack started on 24 February 2022, when Ukraine could have had the right to take defensive action in anticipation of the attack. The question is entirely hypothetical, as Ukraine did not invoke any right of anticipatory self-defence, and, in general, States have rarely done so. In legal literature, however, interest in the concept has prevailed.

The right of anticipatory self-defence is often described by a reference to the criteria for self-defence developed in the Caroline case. By these criteria, self-defence is justified if a threat of an attack is “instant, overwhelming, and leaving no choice of means, and no moment for deliberation.” A frequently used example is about an approaching missile, especially if weapons of mass destruction are presumed to be used. So defined, anticipatory self-defence is in fact not very different from the concept of self-defence under Article 51 of the UN Charter. Very few States or scholars claim that Article 51 should be construed to require that the impact of the attack is felt before the target State can take action to defend itself.

When exactly did Russia’s renewed actions against Ukraine cross the threshold of an “imminent armed attack” that could have triggered the right of anticipatory self-defence? As the Russian troops crossed the border and invaded Ukraine in the early hours of 24 February 2022 and missiles were launched against Ukrainian targets, the troops stayed on the Russian and Belarus side of the border for several weeks. From a legal point of view, deployment of forces at the border of another State does not amount to the use of force and is not necessarily even a threat of the use of force. In addition, similar manoeuvres had also taken place in 2021. In February 2022, the feeling of uncertainty was widely shared, and many believed that the deployment of Russian forces at the Ukrainian border was meant only as intimidation.

More elaborate analyses of the concept of imminence pay attention to the internal decision-making process in the aggressor State. Anticipatory self-defence would be justified, for instance, when “the potential aggressor has irrevocably committed itself to attack.” As Professor Milanović has pointed out, it is not easy to apply this criterion to an autocratic State such as Russia. What if the autocratic leader changes his mind at the last moment?

The past military actions of the Russian Federation in its “near abroad” do not make the assessment of an imminent armed attack any easier. An example is provided by the war in Georgia in 2008, which many see as a direct precedent to the aggression against Ukraine. In Georgia, too, Russia had deployed troops in the vicinity of the border before the invasion on 8 August 2008. Having late in the evening of 7 August received information that Russian military vehicles were on their way to Georgia through the tunnel that constituted the only access route, President Saakashvili ordered a military operation, which, in principle, could have fulfilled the criteria of anticipatory self-defence. The responsibility for the break-out of the armed conflict was nevertheless largely attributed to Georgia. Anticipatory self-defence always bears the risk of turning into a wrongful act.

NATO Expansion

A third question is related to the Russian security concerns, which according to its official rhetoric were heavily connected to the eastward enlargement of the North Atlantic Treaty Organization (NATO). “The NATO enlargement” over the years, had allegedly created a threat to which Russia was compelled to respond. What this allegation completely overlooks is that the military alliance’s enlargement has been the result of sovereign decisions by individual States to apply for membership. Such decisions belong to the domaine réservé of each State, and do not create any right of intervention to third States.

It is beyond the limits of this post to delve into the reasons that have led most of Russia’s western neighbours to take this step. It should be recalled, however, that the internationally recognized borders of the Russian Federation have never been violated by its neighbours. The only troops having crossed them with hostile intent are Russian.

Concluding Thoughts

Far from calling into question or extinguishing the peremptory norm against the use of force, Russia’s 2022 expansion of its invasion of Ukraine reaffirms the status and importance of this most fundamental rule of international law. Through international condemnation and resorts by the aggressor itself to associated legal doctrine, the prohibition on the use of force has seen significant reaffirmation and reinforcement. Finally, while this episode has not settled debates concerning the self-defence doctrine of anticipatory defence or whether acts of encroachment can ever be sufficient to activate self-defence, the clear-cut character of Russia’s violations of the jus ad bellum render such debates largely irrelevant to this most concerning and gross breach of international law.


Marja Lehto is Ambassador (International legal affairs) at the Ministry for Foreign Affairs of Finland. This post was written in the author’s personal capacity and does not necessarily reflect the views of Finland’s Ministry for Foreign Affairs.



Photo credit: National Police of Ukraine