War in Ukraine: Time for a Collective Self-Defense?

[Dr Pavel Doubek is a postdoctoral researcher at Institutum Iurisprudentiae, Academia Sinica, Taiwan. He publishes in the field of International Law and Human Rights.]

In the face of unprecedented aggression of the Russian Federation against Ukraine and the civilian population, calls are getting stronger for the international community to impose a no-fly zone over the Ukraine territory and adopt other necessary measures to restore international peace and security. However, given the concern over further escalation of the conflict, NATO has ruled out the possibility of a no-fly zone, emphasizing that this could drag the alliance directly into the conflict and led to a world war.

Below, I look at this dilemma from the viewpoint of the right to collective self-defense, which is well-established under customary international law and exists independently on defense treaties (such as the North Atlantic Treaty) or resolutions adopted by the UN Security Council (SC).

The SC´s draft resolution S/2022/155 deploring the Russian Federation’s military aggression and deciding to withdraw the Russian Federation’s military forces was vetoed by the Russian Federation, deadlocking the SC to take any resolute action. The SC has humbly recognized this incapacity as a failure in its “primary responsibility for the maintenance of international peace and security” and decided to call an emergency special session of the General Assembly (GA). Although the GA is not entitled to take binding action to restore international peace, its resolution A/ES-11/L.1 deplored “in the strongest terms” the Russian Federation’s aggression and demanded it immediately cease its use of force. As said above, NATO rejected any direct military involvement as “not being part of that conflict” but declared a determination to defend its members.

A Right to Collective Self-defense

Article 51 of the UN Charter enshrines a right to individual and collective self-defense (“nothing in the present Charter shall impair the inherent right of individual or collective self-defense if an armed attack occurs against a Member of the United Nations…”). Although there is no doubt that Ukraine is legitimately exercising its right to individual self-defense under this provision, it is less clear what conditions must be met for other countries to lawfully join the military struggle.

As noted above, the right to collective self-defense emerges under customary international law and depends on the fulfillment of its core requirements, irrespective of bilateral or multilateral defense treaties. These are: (1) the existence of an armed attack which is directed against a State entitled to individual self-defense (victim State); (2) notification to the SC of the measures taken and adherence to the “until” clause under art. 51 of the UN Charter; and (3) compliance with principles of necessity and proportionality.

Armed Attack and Victim State

To the first requirement, it is evident that Ukraine is under an unprovoked full-scale military invasion by the Russian Federation, and so it has a customary right to defend itself and ask other States for help. In the Nicaragua case, the ICJ identified two procedural requirements for the lawful exercise of the right to collective self-defense. First, the State under attack must request support. Second, there must be an express declaration of that State of being attacked. Although the customary nature of these conditions are controversial among scholars, they have both been met in the present case. Ukrainian president Volodymyr Zelenskyj has repeatedly declared both an act of aggression by the Russian Federation against Ukraine and sought assistance from the international community, in particular requesting NATO to declare and enforce a no-fly zone.

Notification of the SC and “Until” Clause

Secondly, Article 51 of the UN Charter obliges parties of collective self-defense to immediately report measures taken to the SC and continue in military operation until the SC takes its own action to maintain or restore international peace and security. In this case, the SC cannot be considered a viable international mechanism for restoring international peace due to the veto by the Russian Federation. This is not, however, an obstacle for exercising the defensive measures – they may continue as long as the SC remains inactive and conditions of necessity and proportionality are met. Nevertheless, when the deadlock is broken and the SC restores its authority over international peace and security, the parties to the conflict must to submit to the SC´s resolutions.

Principle of Necessity and Proportionality

Evidently, neither diplomatic negotiation nor harsh economic sanctions have so far convinced Vladimir Putin to cease the aggression and hostilities. Moreover, Russian aggression remained consistent despite its condemnation by 141 States of the GA, opening an investigation for alleged war crimes and crimes against humanity by the ICC Prosecutor, the International Court of Justice´s provisional measures to immediately suspend the military operation of the Russian Federation and the ECtHR´s urgent interim measures calling on Russia to refrain from military attacks against civilians. On the contrary, the humanitarian situation deteriorates every day and civilian objects are common targets of Russian airstrikes including evacuation routes or facilities such as a maternity hospital and theatre in Mariupol. According to recent reports, over a thousand civilians have already been killed and injured during these hostilities.

Therefore, it is clear that since no less invasive measures are effectively capable to end the ongoing aggression and civilian casualties, the employment of collective self-defense satisfies the necessity requirement.

On top of that, a recent shelling of the Zaporizhzhia nuclear power plant (the largest nuclear power plant in Europe) by the Russian military force also raises the need for collective self-defense. Evidently, fooling around with nuclear power in the context of a military conflict (let alone Putin´s order to put Russia’s nuclear force on high alert) directly endangers global security and concerns the international community as a whole. Seen from this angle, collective action may not be justified “only” as a need to assist the victim State (a “collective defense”), but rather to protect the entire world from complete destruction. Hence, the present case could be regarded as “collective self-defense” in the true sense of the term.

The proportionality principle requires that the defense adheres strictly to rules governing humanitarian conduct of war (ius in bello). It must primarily aim to prevent further casualties, protect civilians and safeguard critical infrastructure, such as nuclear power plants. It must in no way turn into a punitive action and must cease immediately once there is a prospect of a peaceful solution.

The Lesser of Two Evils

There is no doubt that under both customary international law and article 51 of the UN Charter, States are entitled to collective self-defense regarding Russian aggression in Ukraine. It is not clear whether it is invoked as a collective action under the NATO alliance or individually by one or several States.

A wavering between non-military sanctions and the use of force under collective self-defense has not produced any visible progress so far. The situation is indeed worsening every day and procrastination in imposing a no-fly zone and to adopt other measures under collective self-defense is costing the lives of innocent civilians. On the other hand, concerns about further escalation of conflict and possible use of nuclear weapons are understandable and such threats should not be underestimated. It is, therefore, a choice between two evils. I personally believe that the use of collective self-defense is the lesser evil in the face of ongoing suffering of civilians and blatant disregard to international law. Be that as it may, it would be absolutely legal and legitimate.