Regulating Military Force Series – A Future for the UN System of Collective Security?


| Feb 22, 2024

Collective security

Editors’ note: This post is a condensed version of the author’s keynote address at the conference “International Law and the Regulation of Resort to Force: Exhaustion, Destruction, Rebirth?” delivered at Palacký University in Olomouc, Czech Republic. It draws on Erika de Wet & Marko Svicevic, “The Military Clauses in the Treaty of Versailles and the Birth of a Collective Security System” in Société Française pour le Droit International / Deutsche Gesellschaft für Internationales Recht, The Versailles Treaty: French and German Perspectives in International Law on the Occasion of the Centenary (Pedone, Paris 2020) p. 149-67.

“The Charter of the United Nations continues to wilt under the relentless assault of the powerful . . . . In one moment it is invoked with reverence by the very same countries who then turn their backs on it in pursuit of objectives diametrically opposed to international peace and security.”

This quotation is from a statement by the Kenyan Ambassador to the United Nations in February 2022 on the eve of the Russian invasion of Ukraine. In so doing, Russia violated fundamental obligations under international law, ranging from the unlawful use of force and the violation of the territorial integrity of Ukraine to serious violations of international humanitarian and human rights law.

The subsequent condemnation of the invasion by the UN General Assembly (UNGA) as aggression in violation of article 2(4) of the UN Charter was therefore on point; as were statements issued by the members of the European Union (EU) describing the invasion as “grossly violat[ing] international law and the principles of the UN Charter.” The United States for its part condemned the invasion as a violation of the rules-based international order. However, as John Dugard illustrated in a 2023 article in the Leiden Journal of International Law (p. 223-32), the United States’ references to “rules-based international order” remains undefined. He, inter alia, notes that whereas EU member States tend to link this term to respect for international law, it is debatable whether the United States considers its notion of a “rules-based international order” as including the UN Charter system and other rules of international law.

In line with this concern, this post makes the claim that it is the persistent ambivalence and at times cynicism of all major powers that have posed the greatest threat to the notion of collective security over the past century and is likely to continue doing so in the immediate future.

At this juncture it is worth recalling that the Covenant of the League of Nations in Part I of the Treaty of Versailles has been described as the first serious attempt in modern times to institutionalize collective security (Tams, para. 1). However, with the vision of hindsight, the absence from the League Covenant of a centralized decision-making procedure for determining acts of aggression and imposing enforcement measures was one of its greatest weaknesses (Tams, para. 30). In addition, it never enjoyed the full support of all great powers, while fluctuating membership further undermined the League’s work. Ultimately the League’s members failed it (Tams, para. 4).

The following paragraphs will illustrate that similar challenges currently face the United Nations system of collective security that succeeded the League of Nations and constitutes the foundation of post-Second World War collective security. One of the biggest achievements of the UN Charter, compared to the League Covenant, was the centralization of decisions pertaining to the use of force with the UN Security Council (UNSC) in accordance with Chapter VII. Yet, major powers have systematically undermined this very achievement, in particular by underpinning seminal post-Cold War UNSC mandates with ambivalent legal bases that made them vulnerable to abusive interpretation. In addition, States, at times through regional organizations, invoke the right to unilateral humanitarian intervention at the expense of the UNSC’s residual responsibility in this regard.

Collective Security under the UN Charter System

The collective security regime provided by the UN Charter also personifies a system in which each State accepts that the security of one as the concern of all (De Wet & Wood, para. 1). The term collective security does not feature in the UN Charter, but is nonetheless often used to refer to the system for the maintenance of international peace and security and the corresponding provisions of regional organizations (De Wet & Wood, para. 3). In the wake of the Second World War, the notion of collective security centered on collective responses to inter-State military conflict. However, particularly since the 2005 “In Larger Freedom-Report,” the United Nations has embraced a broader notion in accordance with which any event or process that leads to “death or a lessen[ing] life chances on a large scale” (para. 78) can pose a threat to international security.

The system of collective security under the UN Charter is reflected in its provisions concerning the maintenance of international peace and security. These include in particular the prohibition of the use of force in article 2(4) of the UN Charter, combined with the exceptions embodied in Chapter VII. As is well known, these include the inherent right to individual or collective self-defense in article 51 of the UN Charter, as well as the competence of the UNSC to authorize non-military as well as military measures in accordance with articles 41 and 42, respectively, in instances where the UNSC determined the existence of a threat to or breach of the peace or an act of aggression.

It is worth recalling that in accordance with Article 43(1) of the UN Charter, member States undertook to make armed forces available to the UNSC at its request, by means of special agreements. However, as these agreements never materialized, the UNSC developed two different models which in practice consisted of military measures. The first concerns peace-keeping missions under UN command and whose mandates, to the extent that they authorize the use of force (usually for restricted purposes) under Chapter VII of the UN Charter, are based on Article 42.

The second (and from the perspective of this contribution, decisive) category concerns large-scale military operations that are authorized by the UNSC, but executed under so-called “unified command and control” (Blokker, p. 543 et seq.). In these instances, the UNSC authorizes individual States or coalitions of States under Chapter VII to engage in large-scale military operations on its behalf. The authorization model was first used during the Korean war in 1950 and then subsequently revived after the Cold War in UNSC Resolution 678 of November 29, 1990 (Blokker, p. 543 ). This by now legendary resolution authorized the use of “all necessary means” to ensure the withdrawal of Iraq from Kuwait. Thereafter this model became a well-established practice within the UN system for collective security, including authorizations to regional arrangements, such as the North-Atlantic Treaty Organization (NATO).

While the authorization model constituted a key development in the UN collective security system in order to facilitate large-scale military interventions, it simultaneously presents one of the main challenges to the central role of the UNSC in authorizing and overseeing the exercise of the use of force under the UN Charter system. Stated differently, the authorization model represents a contradiction. On the one hand it has become the only viable model for facilitating large-scale military operations with the blessing of the UNSC. At the same time, the authorization model carries with it the possibility of undermining the collective character of military mandates associated with the UNSC. This relates to ambivalence regarding the exact legal basis of such authorizations, as well as abusive interpretations of military mandates by those executing them on behalf of the UNSC. In addition, individual States and regional organizations, have attempted to claim a right to unilateral humanitarian intervention.

Challenges to Collective Use of Force under the UN Charter System

Ambivalent Legal Bases of UNSC Authorizations

Ambivalence regarding the exact legal basis for the authorization model relates to the fact that the UNSC, as a rule, does not specify the UN Charter article(s) on which it relies. It instead authorizes the use of “all necessary means” or “all necessary measures” after referring to the fact that it is “acting under chapter VII,” but without indicating the exact article. The most obvious basis for authorizing States to engage in military operations on its behalf can be found in Article 42 of the UN Charter (Gill, p. 100). However, another possible basis within Chapter VII of the UN Charter would be the right of self-defense recognized in Article 51 of the UN Charter.

In fact, some have argued that the authorization of the use of force against Iraq in UNSC Resolution 678 (1990) was an exercise of the right to self-defense recognized in Article 51 of the UN Charter. Those supporting this reasoning point to the fact that the invasion of Kuwait constituted an armed attack that laid the ground for the exercise of the right to individual or collective self-defense (Dinstein, p. 338). As a result, the coalition of States cooperating with Kuwait need not have sought a UNSC authorization in advance. Yet, obtaining prior UNSC support for their exercise of collective self-defense ensured legal certainty. Stated differently, UNSC Resolution 678 (1990) did not constitute an autonomous basis for military action, but rather “confirmed” the right to self-defense as the basis for military action against Iraq (Dinstein, p. 339).

However, those favoring Article 42 of the UN Charter as the basis of the authorization note that Article 51 is not intended to be applied by the UNSC itself. Instead, it is to be invoked by States (either individually or collectively) when falling victim to an armed attack and before UNSC enforcement action. As a result, a victim of an armed attack can defend itself with the support of other States without prior authorization by the UNSC (Gill, p. 93). But once the UNSC authorizes the use of force, it does so on the basis of Article 42 of the UN Charter.

The question whether Article 42 rather than Article 51 of the UN Charter constituted the legal basis for the authorization to use force in UNSC Resolution 678 (1990) has a bearing on who decides whether the purpose for which the military action has been authorized has been achieved, as well as whether the authorization to use force has therefore ceased (Lobel & Ratner, p. 127-28, 150). This in turn has a direct bearing on the extent that the exercise of the use of force remains centralized with the UNSC. If the UNSC as a collective entity authorized States to use force on the basis of Article 42 of the UN Charter, the decision regarding the termination of this authorization also rests with the UNSC (Lobel & Ratner, p. 128). In line with this argument, the authorization to use military force in UNSC Resolution 678 (1990) ceased with the adoption of UNSC Resolution 687 (1991): by affirming the formal ceasefire, it confirmed that the purpose of the military authorization has been achieved ( Lobel & Ratner, p. 148-49).

However, according to those who argue that the military action subsequent to UNSC Resolution 678 (1990) was rooted in Article 51 of the UN Charter, any such decision rests with the States that invoked the right to individual or collective self-defense (Dinstein, p. 339). Thus, the cease-fire between Kuwait and its allies and Iraq suspended hostilities, but did not terminate the war (Dinstein, p. 340-41). Kuwait and its allies could still invoke the right to self-defense in instances of a material breach of the cease-fire by Iraq. In accordance with this reasoning, the United States and the United Kingdom relied on UNSC Resolution 678 (1990) as the basis for a variety of aerial attacks on Iraq during the 1990s. It also set the stage for the large-scale invasion of Iraq by the United States and the United Kingdom in 2003 (Dinstein, p. 341-43).

Opinions among authors and States remain divided as to whether Article 51 indeed constituted the legal basis of Resolution 678 (1990). From the perspective of the centralization of the use of force, the utilization of the right to self-defense as an instrument of collective security results in a paradox. The very organ (the UNSC) whose primary purpose is to centralize decisions pertaining to the use (and termination) of forcible measures, instead relies on the right to self-defense which is by nature decentralized. In so doing, the UNSC actively undermines its own centralizing role as it explicitly encourages unilateral decisions on the use of force by States.

Another more recent manifestation of this paradox may be found in UNSC Resolution 2249 of 20 November 2015 pertaining to the Islamic State (IS). This resolution was neither adopted under Chapter VII of the UN Charter, not did it explicitly invoke Article 51 of the UN Charter as an instrument for collective security. Instead, paragraph 5 merely calls upon States to use “all necessary means” within the IS-controlled areas in as far as international law allows (Akande & Milanovic). Yet, when subsequently invoking Article 51 of the UN Charter in relation to IS, Germany, Belgium, Denmark, Norway, and the United Kingdom made reference to UNSC Resolution 2249 (2015). This suggests that the resolution implicitly encouraged States to invoke the right to self-defense in relation to IS in Iraq and Syria. In so doing, the UNSC once again undermined its own centralizing role in relation to forcible measures.

Abusive Interpretation of Chapter VII Mandates

UNSC Resolution 678 (1990), combined with its follow up resolutions pertaining to Iraq, is also a prominent example of how abusive interpretation of UNSC resolutions can distort the purpose of a military authorization. Another pertinent example is UNSC Resolution 1973 of 17 March 2011 concerning Libya. As far as Iraq was concerned, the decentralized interpretation of UNSC Resolution 678 (1990) by those States regarding Article 51 of the UN Charter as the basis for the authorization to use force, combined with a distortive interpretation of its purpose as well as that of UNSC Resolution 1441 of 8 November 2002, paved the way for the illegal 2003 invasion of Iraq. The respective States claimed that the adoption of UNSC Res 1441 (2002) permitted them to determine individually whether Iraq had engaged in a material breach of prior UNSC resolutions, thereby reviving the authorization to use force (Dinstein, p. 341-42).

However, the text and context of the resolution made clear that it was for the UNSC as a collective organ to consider whether any material breach had occurred. The joint statement adopted by three permanent members (China, France, and Russia) to explain their vote on Resolution 1441 (2002) also confirmed that it did not authorize resort to force. Moreover, it remains unclear what material breach Iraq had actually committed prior to the 2003 invasion, as accusations of the existence of weapons of mass destruction remains unproven until this day. Instead, the invasion seems to have been based on the 2002 United States National Security Strategy (“Bush doctrine”), according to which self-defense can be triggered by a vague, non-imminent threat that may occur at some unspecified point in the future.

A Chapter VII authorization underpinned the invasion of Libya in 2011. UNSC Resolution 1973 of 17 March 2011 (para. 4) authorized air strikes for the protection of civilians under threat of attack, thereby endorsing the residual responsibility of the UNSC to protect populations within States against mass atrocities (responsibility to protect, or R2P). Nonetheless, the subsequent regime change in Libya was criticized, including by the BRICS (Brazil, Russia, India, China, and South Africa) States, as overstepping the mandate (Ulfstein &Fosund Christiansen, p 166-67). The resulting fallout within the United Nations resulted in a backlash against the R2P concept within the UNSC and has made it increasingly difficult to adopt any coercive Chapter VII measures in relation to major international armed conflicts (Garwood-Gowers, p. 609-10). While the fear of abusive interpretation of UNSC resolutions by individual permanent members may not have constituted the only factor blocking UNSC coercive measures against, for example, Syria, it was a contributing factor (Garwood-Gowers p. 612-13).

Ironically, the resulting stalemate in the UNSC in turn contributed to the extensive use of the right to self-defense in Syria by in particular western States, which—whatever its merits may be—further eroded the centralization of the use of force within the UNSC. It also reignited the debate about the legality of so-called humanitarian intervention: i.e., the right to unilateral forcible measures in third States, “for the purpose of preventing or putting to a halt gross and massive violations of human rights or international humanitarian law” (Ryniker, p. 528).

Claiming the Right to Humanitarian Intervention

Since the late twentieth century, such military interventions were initiated in particular by regional organizations in Africa, as well as NATO member States. For example, the Economic Community of West African States (ECOWAS) intervened in Liberia and Sierra Leone in the 1990s in the absence of a prior Chapter VII UNSC resolution, which contradicted the clear language of Article 53(1) of the UN Charter. One of the justifications forwarded at the time related to the human rights atrocities committed in the respective countries (Levitt, p. 334 et seq.). Similarly, the unauthorized NATO intervention in Kosovo in 1999 was motivated (even explicitly by some States) by grave humanitarian concerns (Paddeu, p. 652-53).

Subsequently, the African Union (AU) in Article 4(h) of its Constitutive Act of 2000 and ECOWAS in article 25 of its 1999 Protocol on Conflict Prevention institutionalized a right to humanitarian intervention in member States, both documents leaving open whether prior UNSC authorization is indeed required. However, in practice, all interventions under the auspices of the AU or ECOCWAS have thus far either been backed by UNSC Chapter VII resolutions or the consent of the recognized government.

The NATO intervention in Kosovo, in fact, constitutes the only open challenge to the central authority of the UNSC by a regional organization on the basis of humanitarian concerns. As far as individual States are concerned, the United Kingdom explained its (somewhat symbolic) April 2018 aerial attacks in response to Syria’s alleged use of chemical weapons as an exceptional measure in the face of “overwhelming humanitarian necessity.”

Implications for Ukraine and Beyond

By the time of the expanded Russian invasion of Ukraine in February 2024, the conduct of powerful States had already considerably weakened the capacity and credibility of the United Nations system for collective security. Unfortunate precedents set by western States in Iraq and Libya were very cynically continued by the Russian regime. In fact, when announcing the so-called “special military operation” on November 24, 2022, President Putin specifically referred to the bombing of Belgrade during the Kosovo intervention, the 2003 invasion of Iraq, and the distortion of the Libya mandate in 2011 (Milanovic).

He further invoked the right to self-defense in Article 51 of the UN Charter in a manner reminiscent of the “Bush doctrine” of 2002. To this end he, inter alia, referred to the development of biological weapons in Ukraine with the financial assistance of the United States, as well as the need for humanitarian intervention in response to (in his view) an ongoing genocide in eastern Ukraine (Milanovic).

That these claims were baseless and deeply cynical transpires from the UNGA’s March 2022 resolution that condemned the Russian aggression against Ukraine. For current purposes it suffices to state that neither NATO nor Ukraine engaged in an armed attack against Russia. Nor was there any evidence that it threatened to do so, whether by unleashing biological weapons or otherwise. Also, while there were human rights abuses on all sides in the separatist regions of eastern Ukraine since 2014, Russia had not presented any credible evidence of genocide.

Yet, at the same time, Russia’s conduct and discourse highlights the destructive dynamic that can be triggered when powerful States carve out exceptions to the prohibition of the use of force in order to serve their own interests. Once such a precedent has occurred, more will follow. As a consequence, complete erosion of collective security becomes only a matter of time.

Thus far, the collective security model envisaged by the UN Charter has proven to be more robust than that of the League of Nations Covenant. Over a period of almost 80 years, it has shown itself capable of evolution and revival. Most recently, UNSC Resolution 2699 of October 2, 2023 concerning Haiti provided a shimmer of hope in this regard. Even so, the greatest achievement of the UN Charter, namely the centralization of the use of force with an organ that engages in collective, binding decision making on behalf of the international community, is increasingly under pressure. In addition, regional and sub-regional organizations have begun to carve out autonomous roles for themselves. While still embryonic, it is conceivable that their security frameworks will evolve and potentially eclipse centralized decision-making withing the UNSC.

Concluding Thoughts

The early twenty-first century has witnessed a resort to unilateralism by major powers at the expense of the UN Charter system, in a manner that is reminiscent of the demise of the League of Nations. In order for meaningful centralized decision-making within the UNSC to be revived, a clear paradigm shift amongst all major powers is necessary. Although any such shift appears highly unlikely, it does not have to mean that it is impossible. History has taken very unexpected turns for the better in the past and may do so again. Hopefully an unexpected turn towards collective security will occur in time to salvage what is left of the cornerstone of the United Nations collective security system.


Erika de Wet is Professor of International Law and Head of the Institute of International Relations in the Faculty of Law, University of Graz, Austria and Honorary Professor in the Faculty of Law, University of Bonn, Germany.




Photo credit: Spc. DeAndre Pierce