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As states invoke “self-defence” to justify aggression, Article 51 of the UN Charter risks becoming a tool for legitimising war, not preventing it.
In the aftermath of World War II and the collapse of the League of Nations, the United Nations (UN) was established to prevent the recurrence of global armed conflicts. Its Charter enshrines a simple but profound rule in Articles 2(3) and 2(4): states must resolve disputes peacefully and refrain from the threat or use of force against one another. In layman’s terms, it means that all UN member states are under a legal obligation not to wage war on another state.
Why, then, is the world witnessing an unprecedented surge in interstate conflicts in nearly four decades? From Russia’s invasion of Ukraine to Israel’s ongoing operations in Gaza, trends from the past two decades are signalling the gradual normalisation of coercion as a policy tool. What is most striking, however, is not merely the frequency of such conflicts, but the legal justifications offered for them. Both aggressors and defenders now claim to act in the name of self-defence and national interest. Russia invoked Article 51 to justify its invasion of Ukraine; Israel relies on the same provision to defend its assault on Gaza following Hamas’s 7 October 2023, one that the UN mission denounced as genocidal.
What is most striking, however, is not merely the frequency of such conflicts, but the legal justifications offered for them.
This widespread invocation of self-defence by all sides, regardless of context, reveals how a legal safeguard has evolved into a strategic instrument. Originally intended as a narrow exception to the prohibition on the use of force, the right to self-defence under Article 51 has been reinterpreted so broadly that it risks becoming a rhetoric. It becomes vital, then, to understand why and how this transformation of the meaning of Article 51 has occurred, the answer to which lies in its two interpretations.
The restrictive interpretation focuses on fulfilling the condition of the occurrence of an ‘armed attack’ as well as what constitutes one. According to this interpretation, a state’s prerogative to defend itself kicks in only if armed forces of another state have crossed its border, and that too only until the Security Council takes necessary measures to restore peace, as stated in the Article. The negotiation history of the right to self-defence supports this interpretation.
On the other hand, the expansive interpretation states that the right to self-defence can also arise in case of an ‘imminent threat’ of an armed attack. Detailing this expansive definition, Article 51 does not exclude the right to self-defence in case of an imminent threat, and the right to anticipatory self-defence is, in fact, necessary in today’s world. This interpretation also leaves a wider scope for a state to adopt the right to self-defence in relation to who was attacked, by whom, and how. This is why the right to self-defence is being used as a legal shield for questionable actions of states.
Until the 9/11 episode, only the United States (US) and a few of its allies—including Israel and the United Kingdom (UK)—supported this interpretation. The rest of the world largely supported the restrictive interpretation. However, the incidents of 9/11 and Washington’s response in the form of prolonged armed operations in Afghanistan have impacted the loosening legal constraints on the right to self-defence, expanding its scope against non-imminent attacks, namely the doctrine of pre-emptive self-defence. This new, relatively dangerous approach was showcased in Operation Iraqi Freedom (2003), when a US-led alliance invaded Iraq and overthrew Saddam Hussein under the pretext of his support of terrorists and, most importantly, possession of Weapons of Mass Destruction (WMD). Both of which were proven to be absolutely false. It was not as though the world accepted the US and its allies moulding international law to their will. Yet, while few endorsed their move, most also refrained from condemning it, granting the wide interpretation of the right to self-defence a tacit approval.
While few endorsed their move, most also refrained from condemning it, granting the wide interpretation of the right to self-defence a tacit approval.
Since then, the scope of Article 51 has only expanded, with the right to self-defence being cited against actions of non-state actors based in another UN state, such as terrorist groups. While the International Court of Justice (ICJ) in its 2004 Wall Advisory Opinion states that such an interpretation does not find a place in codified international law, as seen in the Nicaragua case, it also recognises the evolving nature of Article 51, which can be reinterpreted based on state practices over time.. Even the UN Security Council has mentioned the right to self-defence in case of attacks by a non-state actor, such as Al-Qaeda. In fact, the US, in particular, has also adopted this expansive interpretation to justify its operations against non-state actors in Syria and Afghanistan.
What this means is that while the original scope of Article 51 may have been restrictive, state practice, led by the West, has expanded its scope to a point where a state can cite the right to self-defence when attacking another state or a non-state actor, even if there is simply a possibility of a threat and no prior attack has occurred. Those in support cite the technological advancements in weapons, nuclear threats, as well as the emergence of threats from non-state actors, as modern requirements for such a wider interpretation.
While the arguments in favour of a broader interpretation of the right to self-defence are certainly compelling, such an approach has eroded the very foundations of the international legal order that emerged from the ruins of World War II. The expansive reading of Article 51, once an exception to the prohibition on force, has translated into a legal instrument of convenience, enabling states to legitimise aggression under the guise of preemption or prevention.
By stretching the notion of “self-defence” to include perceived or speculative threats, states have inverted the Charter’s logic, making the exception the rule.
This shift undermines the central purpose of the UN Charter: to make peace the norm and war the last resort. International law is not designed to accommodate every strategic anxiety of states; it is meant to restrain them. By stretching the notion of “self-defence” to include perceived or speculative threats, states have inverted the Charter’s logic, making the exception the rule.
If the international community continues to accept and employ such broad interpretations, the prohibition on the use of force faces the danger of collapsing into irrelevance. To preserve a world order committed to peace, a return to a restrictive interpretation of Article 51, one anchored in necessity, proportionality, and imminence, is essential.
Udayvir Ahuja recently completed his LLM in International Law from SOAS, University of London, where he focused on contemporary issues at the intersection of international law, geopolitics, and global governance. He was a Programme Coordinator for the Strategic Studies Programme, Observer Research Foundation
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Udayvir Ahuja recently completed his LLM in International Law from SOAS, University of London, where he focused on contemporary issues at the intersection of international ...
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