Overview of the doctrine of self defence


1.1 :- Interplay between Articles 2(4) and 51 of the UN Charter:-

On September 11, 2001, the United States was attacked. Hijackers turned passenger planes into missiles and used them to destroy the World Trade Center and to damage the Pentagon. President Bush made clear the United States would respond forcefully against those responsible. High ranking members of the administration encouraged the use of force against any states known to be linked to terrorist groups. But in a move for which the administration received great international praise with respect to action following September 11, it waited. In the days following the attacks, it established that the perpetrators were all members of the Al Qaeda terrorist organization. On October 4, the British government released a study showing the close ties between al Qaeda and Afghanistan’s de facto government. On October 7, 2001, Operation ‘Enduring Freedom’, a massive air operation, including some ground forces, was launched against Afghanistan. Both the US and the UK notified the UN SC that ‘Enduring Freedom’ was an exercise of individual and collective self-defense in compliance with the terms of United Nations Charter Article 51, which permits the use of force in self-defense against an armed attack [1] . [2] 

Self-Defence is commonly any act in response to an imminent threat of death or grave bodily harm to person or property. This right is however not just limited to individuals and is also available to States. The concept of Self-Defence has been an important doctrine of International Law which has again gained importance in the light of growing acts of illegal use of force threatening world peace and security. Thus it becomes important to clearly understand this doctrine as it exists today and its application to the modern world. [3] 

In the wake of World War II participants at the Dumbarton Oaks and San Francisco conferences determined that unlike the covenant of the League of Nations the United Nations [4] Charter, which is one of the world’s most important treaties and ratification of which is a prerequisite to membership of the United Nations, should outline war. To this end they agreed that States should accept the obligation to settle all disputes amicably and to refrain from the use of force in their international relations.

Article 2(4) of the UN Charter states: [5] 

“All Members shall refrain in their international relations from the threat or use of force against the territorial integrity or political independence of any state, or in any other manner inconsistent with the purposes of the United Nations."

Essentially, this eliminated the concept of a ‘just war’. [6] The use of force, or the threat of it, by a state is no longer a legitimate means of dealing with a dispute with another state. Despite this one thing which was clear was the States determination and competence to repel attacks by the use of force. [7] For this purpose the existing Right of Self-Defence was codified and set out in Article 51 (Chapter VII) of the UN Charter, in the form of the “Right of Individual and Collective Self Defence", thus creating an exception to the general rule prohibiting the use of force.

Article 51 of the UN Charter states: [8] 

“Nothing in the present Charter shall impair the inherent right of individual or collective self-defence if an armed attack occurs against a Member of the United Nations, until the Security Council has taken measures necessary to maintain international peace and security. Measures taken by Members in the exercise of this right of self-defence shall be immediately reported to the Security Council and shall not in any way affect the authority and responsibility of the Security Council under the present Charter to take at any time such action as it deems necessary in order to maintain or restore international peace and security."

1.2 :- Contemporary Significance:-

Since the entry into force of the UN Charter, self-defence is used as an excuse by the States to justify use of force, for in principle, use of force is banned not only by the Charter but also by modern constitutions. [9] The events of 11 September and the subsequent adoption by the United States of a doctrine of pre-emptive, or even preventive, self-defence as part of its national security strategy, and its partial reliance upon that doctrine to justify the recent war against Iraq, has caused a great deal of controversy at both the diplomatic level and among international legal scholars relating to the permissibility of anticipatory or preventive self-defence in advance of an armed attack. Much legal opinion seems to agree that self-defence is permissible in response to an immediate and manifest threat of an attack, but opinion diverges sharply on whether self defence is permissible in response to potential threats of an attack, such as terrorist threats and the possible use of weapons of mass destruction by terrorist organisations. [10] Controversial points include such questions as what constitutes an immediate threat of an armed attack, what is the proper interpretation of the relationship between Charter law and customary law relating to self-defence and what is the proper and desirable relationship between the right of self-defence and the rest of the law governing the use of force? [11] 

For this purpose the researcher will first explain the entire concept of Self Defence as it existed under customary international law and as it exists under Article 51. The researcher will also deal with the several controversial interpretational issues of this doctrine and its application. The researcher also examines how States are stretching the notion of this permissible use of force to justify their armed actions in foreign territory. Finally the researcher will deal with the question of Self-Defence against acts of Terrorism.

The starting point is that self-defence is a right, grounded in both Charter and in customary law, which allows some degree of anticipatory action to counter a clear and manifest threat of attack in the immediate, or at least proximate, future, within the confines of the well known and widely accepted 1837 Caroline incident criteria, relating to necessity, immediacy and proportionality. [12] These criteria though they still provide a workable and acceptable framework for analysis, are not a substitute for analysis itself. In short, they must be applied in the light of other factual and legal considerations and were never meant to be, nor can they be seen in isolation as mere abstractions, without due regard for the relevant circumstances of each particular situation.

1.3 Aims and Objectives:-

This project aims to study and analyse the legal evolution and establishment of the concept of Self Defense, as an aspect of International Legal Jurisprudence, using Terrorism as an illustration. In the present paper the researcher has exhaustively analysed the Right of Self-Defence as it existed pre and post the coming into force of Article 51 of the UN Charter. The researcher has also dealt with several controversial issues attached with Article 51, such as anticipatory self-defence. Finally, in light of growing terrorism and counter terrorism, the researcher has looked at the Right of Self Defence against acts of Terrorism, as this occupies extraordinary importance in contemporary times as was made clear by the 9/11 terrorist strike and post that the Afghanistan and Iraq wars.

1.4 Research Methodology:-

The researcher has adopted the doctrinal form of research in completing this project. As the project is primarily a descriptive analysis, the doctrinal form of research was most appropriate. Primary as well as secondary sources of information have been used from the NALSAR Law Library. The above category of material consists of commentaries like that by Brownlie and Oppenheim, cases and websites like JSTOR, Westlaw etc. No part of this project is plagiarized and it is the original work of the researcher.

1.5 Research Plan:-

Chapterization: The researcher has divided the project into the following chapters.

Introduction- this provides the reader with an abstract introduction of the topic in brief and the issue at hand. It looks to familiarize the reader with the researcher’s plan and his objective.

General overview of the Doctrine of Self-Defence- this consists of an exhaustive study of the law of Self Defence in international law

Aspects of the Law of Self-Defence- this deals with the various controversial issues and interpretations such as anticipatory Self Defence.

Conclusion- this finally concludes the topic by answering the questions raised earlier and also includes the researcher’s opinion on the issue.


2.1 : General Overview:-

2.1.1: Traditional:-

The traditional law of self-defence was interpreted in a very broad way before the entry into force of the Charter of the United Nations (UN). [13] Nineteenth century treaties did not generally prohibit the use of force, and thus self-defence required no definition. At those times, States enjoyed a right to wage war without any limitations. [14] Recourse to war to solve international controversies was outlawed by the Paris Pact (the Kellogg-Briand Pact) in 1928, although the two treaties lacked a definition of self-defence and the concept was not even mentioned. [15] However, in the diplomatic correspondence before the ratification of the Pact, the UK made clear that it did not impair the right of self-defence, which was a right to defend the security of any part of the British Empire. [16] 

2.1.2: Modern:-

This situation completely changed with the drafting of the United Nations Charter. Not only did it prohibit the threat and use of force, thus shifting the focus from war to force, but also defined self-defence as a right which could not be impaired by prohibitions on the use of force. [17] According to the original system of the UN Charter, collective security was in the hands of the Security Council. States, if attacked, were permitted to act in self-defence against the aggressor until the Security Council intervened. The framers however failed to substantiate the concept of self-defence, and nowadays, States exercise their right of self-defence to justify use of force for mainly three reasons [18] :

• Use of force has been completely prohibited by the Charter, and accordingly, self-defence is thus invoked even though it is in effect a violation of the UN Charter;

• States have been obliged to rely on their own means in defending themselves against external aggression due to the collapse of the UN security system; and

• Modern constitutions generally forbid war and use of force in violation of international law, and hence, self-defense helps overcome these constitutional constraints.

To avoid accusations of aggression, States rely on Article 51 of the Charter by claiming an inherent right of self-defence, which provides in part: “Nothing in the present Charter shall impair the inherent right of individual or collective self-defence if an armed attack occurs against a Member of the United Nations, until the Security Council has taken measures necessary to maintain international peace and security" or a right of “humanitarian intervention" under customary international law, when they lack express authorization from the Security Council acting under its enforcement powers provided for in Chapter VII to use force against another State.

Self-defense can best be understood by its defining features. First, under Article 51 of the U.N. Charter, it is described as a “right" not an obligation and therefore States generally have the freedom to exercise it. Second, it is recognized as a “legitimate form of armed self-help" [19] , thus allowing States to lawfully use force on their own authority. Third, it is available either individually or collectively and hence it can be invoked by a single State, by two States jointly, or under a multilateral arrangement. Fourth, it is not confined to survival situations and hence self-defense may be lawful resorted to even in non-catastrophic scenarios. [20] 

2.1.3: Different from self-preservation or necessity:-

To properly understand the nature and scope of self-defense, one must also distinguish it from the related doctrines of self-preservation and necessity. [21] Like self-defense, these doctrines are used to justify the use of force, but their conception is vague and too expansive to provide a minimum standard. Historically, these notions were closely linked with self-defense, but by the 1950’s, their “mutual identity had eroded and self-defense was viewed as a separate and more limited concept." [22] 

Under international law, self-defensive force must observe two chief principles: necessity and proportionality. Necessity requires that States resort to force as a sole resort available to defend itself against a threat. This implies that a State must exhaust all other measures to avert the use of force, such as diplomatic negotiations, imposing economic sanctions or unarmed intervention by the UN SC. [23] Furthermore, states must also exhibit both that the external threat is real and that peaceful means have been exhausted. [24] 

Proportionality is the second fundamental principle underlying self-defense and its meaning depends on whether it is applied in the context of jus ad bellum or jus in bello. In cases of jus ad bellum, proportionality does not refer to equality between the quantum, intensity or means of force, rather it is understood as the degree of force strictly required to repel a given threat. [25] 

2.2 The Caroline Doctrine:-

The Caroline incident is generally regarded as the reference point for any discussion on self-defence, as well as the criteria governing its use. [26] In 1837, US Secretary of State Daniel Webster articulated a definition of self-defence, which evolved into customary international law. [27] Webster’s definition followed what has come to be known as the Caroline incident. The Caroline was a US steamboat attempting to transport supplies to Canadian insurgents. [28] A British force interrupted the Caroline’s voyage, shot at it, set it on fire and let it wash over Niagara Falls. Webster said that Britain’s act did not qualify as self-defence because self-defence is only justified “if the necessity of that self-defence is instant, overwhelming, and leaving no choice of means, and no moment for deliberation." This incident is important primarily for the following reasons: [29] 

First, to limit self-defence to situations where the threat is real, the response is essential and proportional, and peaceful means have been exhausted. Article 51 further narrowed self-defence, permitting it only in case of an armed attack. Second, it laid down the general framework for exercising self-defence, including anticipatory self-defence. Acceptance by British and American governments of self-defence as relevant in situations of necessity in anticipation of a threat of attack which was ‘instant, overwhelming, leaving no choice of means and no moment for deliberation’ clearly indicates that anticipatory self-defence formed part of traditional customary law. [30] Third, reference to this general framework by the Nuremberg and Tokyo Tribunals demonstrate that they were still considered customary law, as the Charter was being framed. [31] 

As most authorities accept this as a given and since there is no evidence that the Caroline framework has been replaced by conventional law, we can safely assume that ‘Caroline’ still forms part of the customary law relating to self-defence. This, then permits States to respond to a threat and infringe on the territorial sovereignty of another nation when: (i) it is acting in self-defence, (ii) the attack is substantial, (iii) the offending nation is unable to prevent further attacks and (iv) the attack is widespread and imminent. [32] 

2.3 Article 51, UN Charter:-

The UN Charter, so as to avoid the horrors of the World Wars, seeks to establish a world order free from armed conflict. It requires States to peacefully resolve their conflicts. The purpose of the United Nations is to save the succeeding generations from the scourge of war. [33] “All members are required to settle their international disputes by peaceful means and to refrain in their international relations from the threat or use of force against the territorial integrity or political independence of any state, or in any other manner inconsistent with the Purposes of the United Nations." To that end, the UN Charter sought to limit when states could act in self-defence.


3.1 Pre-emptive and Anticipatory Self Defence:-

Traditional state v state war is largely a relic. How then does a nation-state defend itself, pre-emptively, against an unseen enemy? Existing international law--the Caroline Doctrine, UN Charter Article 51, Security Council Resolutions 1368 and 1373--do not provide sufficiently clear guidelines regarding when a state may take pre-emptive or anticipatory action against a non-state actor. [34] There are two contrasting interpretations on the content of the right of self-defence:

3.1.1 Restrictive interpretation:-

Those favouring the restrictive interpretation of article 51 focus on the qualifying phrase ‘if an armed attack occurs’ and what constitutes an ‘armed attack’. They claim that the use of force is expressly limited to cases where the armed attack has already commenced. Armed attack is interpreted to mean, ‘once the armed forces have crossed the border into another state’. They argue that while customary IL prior to the Charter may have allowed self defence in anticipation of an armed attack, Article 51 limits the scope of that right. Self-defence is now only allowed in response to an ‘armed attack’ against a state and does not include anticipatory self-defence. Any use of force in self defence shall be reported to the Security Council immediately, which shall take necessary measures. The right to use force in self-defence thus seems an independent but transitory right and hinges on the occurrence of an armed attack. [35] 

Professor Kunz argues that article 51 ‘constitutes an important progress by limiting the right of ... self-defence to the one case of armed attack against a member of the U.N.’. ‘This right does not exist against any form of aggression which does not constitute ‘armed attack’ and it ‘means something which has taken place’. [36] Professor Gross argues that ‘the wording of Article 51 requires an armed attack using weapons and that mere threats or declarations are insufficient ... The indispensable condition for the exercise of the right of ... self-defence under article 51 of the Charter is that ‘an armed attack occurs’. [37] 

3.1.2 Expanded interpretation:-

Contrary to the above interpretation, a significant number of publicists argue that force may not only be used in self-defence, in response to an armed attack but it may also be used in response to an ‘imminent threat’. They argue that self-defence is both a customary right and a treaty right. Customary law lives side by side with conventional law. Under customary law, anticipatory self-defence is permissible when the threat of an armed attack is ‘imminent’. The Charter codifies the pre-existing customary rule of self-defence but does not exhaust it. Hence, the right to anticipatory self-defence exists and states may rely on customary rule or Charter or both of them. [38] 

Professor Waldock argues that to say self-defence begins only ‘if an armed attack occurs’ is to go beyond the intended meaning of the word. It was not the intention of the framers to narrow down the right to self-defence beyond the doctrine of the Caroline (1837) incident. [39] Professor Bowett reaffirms that article 51 does not exclude an action taken against an imminent threat. [40] Professor Schachter cautiously says that it is erroneous to say that article 51 completely excludes anticipatory self-defence as it is not clear whether it was intended to cut down the inherent right to self-defence under customary law. [41] 

3.1.3 International Position:-

Both the International Court of Justice (ICJ) and the International Law Commission (ILC) have failed to clarify the position. The ICJ has issued two advisory opinions in which the use of force was involved, including the right of self-defence: the recent Oil Platform case involving Iran and the United States, the Opinion on the Construction of a Wall in the Palestinian Territories and the Case Concerning Armed Activities in the Territory of the Congo. However, the ICJ did not clarify whether a right of anticipatory self-defence was available to States. In the Nicaragua case, the Court was obliged to decide the dispute according to customary international law and said that the Charter’s provisions on the use of force coincided with customary IL, although the Court did not look into anticipatory self-defence because it was not an issue for adjudication. [42] Nor has the ILC resolved the issue. In its Draft Articles on State Responsibility, the ILC lists self-defence one of the circumstances precluding wrongfulness (article 21). However, it abstained from resolving the point under discussion.

The content of the right of self-defence was raised during the attempts made to reform the UN Charter. The High-Level Panel appointed by the UN Secretary General has taken a position on the lawfulness of the right of anticipatory self-defence. In its Report on Threats, Challenges and Changes, dated 1 December 2004, [43] the Panel supports the interpretation embodied in the theory of ‘anticipatory self-defence’, which allows for reaction when the attack is imminent (missiles do not necessarily have to hit the attacked State’s territory, and the State can react if preparations for their launching are underway). However, the Report rejects the doctrine of pre-emption theorized by the US President George W. Bush in the 2002 US National Security Strategy [44] document. According to the Report, the existence of a mere threat to security is not sufficient to make an armed reaction legitimate. The attack has to be imminent. Thus, the mere acquisition of weapons of mass destruction by one State, while constituting a threat to security, does not give another State the right to react in self-defence. The speculation on the possible use of force against Iran with a view to preventing that State from acquiring a nuclear capacity, which has circulated within the US administration in the early months of 2006, cannot be subscribed to in legal terms. [45] 

The High-Level Panel’s report rejects the notion of ‘pre-emptive self-defence’ advocated by President Bush, which would allow action to be taken against ‘rogue States’, terrorists and States possessing weapons of mass destruction. The report specifically states that article 51 of the UN Charter need neither be rewritten nor be reinterpreted. However, it does interpret article 51 in a way that UN bodies have been loath to do until now. In his subsequent report, the UN Secretary General endorsed the point of view of the High-Level Panel and stated ‘imminent threats are fully covered by Article 51, which safeguards the inherent right of sovereign States to defend themselves against armed attack. [46] 

The ICJ in the Congo case [47] rejected the doctrine of pre-emption in response to a latent threat on the ground that it is a matter that falls within the competence of the UN SC which authorizes the use of force, if circumstances so demand. More specifically, the Court stated that ‘Article 51 of the Charter may justify a use of force in self-defence only within the strict confines there laid down. It does not allow the use of force to protect perceived security interests beyond these parameters. Other means are available to a concerned State, including, in particular, recourse to the Security Council’.

This is a narrowing of the Caroline doctrine that provided for anticipatory self-defence provided the threat to national security is reasonably imminent. [48] Article 51 has significantly reduced this concept from that under the Caroline doctrine. The significance of this narrowing cannot be underestimated--from a customary international law principle enabling preemption to a treaty-based definition of self-defence grounded in occurrence of an armed attack.

3.1.4 Conclusion:-

With respect to the lawfulness of anticipatory self-defense, it would be fair to say that no clear consensus has emerged, and there are many reasons for this indeterminacy. First, lack of standardized terminology leads to confusion and misunderstanding. Second, the preciously small and often complex historical incidents of State practice are not easily reducible to a single interpretation. Third, the very nature of customary law makes it difficult to evaluate State Practice and Opinio Juris with certainty. Fourth, this issue is strongly political and involves high stakes, including State survival. Finally, due to the lack of any ICJ decision on this issue, we must find our way without clear judicial direction. [49] 

Nevertheless, three clusters of opinion have emerged. Among one, a cluster of States, there is a significant amount of post-charter State resistance to anticipatory self-defense based on the restrictive interpretation, which is expressed vocally and consistently. A second cluster comprises those States that are open to the notion of anticipatory self-defense, but in extremely narrow circumstances, such as the existence of an imminent, if not massive, threat and where peaceful means of resolution have been exhausted. These States tend to align with the Caroline standard and also cite it as authority. Lastly, a relatively small number of States, led by the US and Israel, favour the broader exercise of anticipatory self-defense. [50] 

The researcher is of the opinion that Article 51 did not supersede customary IL, rather recognized and incorporated it [51] and that the language of Article 51 was flexible enough to accommodate anticipatory self-defense. It then becomes possible to revert to the status of customary law as it existed prior to the Charter and in pursuance of this a consensus appears to be developing in favour of a limited degree of anticipatory self-defense.

3.1.5 Suggestions:-

Anticipatory self-defence, as a principle has gained currency even among the tenants of a narrow interpretation of article 51. The High-Level Panel’s interpretation of self-defence must be understood in the light of the development of new weapons and threats. To permit response only once a missile has struck the attacked State and not when preparations for its launch are unequivocally underway would be absurd. [52] 

This requires a new, process-based ‘strict scrutiny’ approach to pre-emptive self defence against non-state actors. This approach allows a State to react early against a non-state actor, as long as the act is based on reliable, viable, and corroborated intelligence as per a court of law. [53] To rephrase, the strict scrutiny test seeks to strike a balance enabling the state to act sooner, but subject to significant restrictions.

With respect to the new triangle of operational counter-terrorism --law, policy and morality-- strict scrutiny enables the state to meet the four principles of international law --collateral damage, proportionality, military assistance and alternatives-- that are the ‘heart and soul’ of the laws of war. By enabling the state to act earlier than is allowed by present IL standards, while subjecting it to the above restrictions, the strict scrutiny test facilitates adherence to the four international principles. [54] 

3.2 Collective Self-Defence:-

Collective self-defence is a right enshrined in the Charter and allowed by customary IL. It allows taking action to help an attacked State, be it a member of the United Nations or not. Its exercise does not depend on whether the intervening State and the victim State are party to a military pact obliging measures to defend the attacked State or not. [55] 

First, the intervening State may take action without the consent of the aggrieved State, does not wish to react, but seeks a peaceful solution of the dispute or it does not want to risk entering into an armed conflict. Thus, an act of collective self-defence requires the request or at least the consent of the attacked State. However, this is not always followed. [56] 

The second area of concern involves instances of intervention for implementing self-determination. However, General Assembly resolutions give only a ‘right of resistance’ to liberation movements. [57] 

Lastly, defensive pact such as NATO may oblige States to take measures in collective self-defence. The Security Council however, has till date only ordered sanctions and other non-forceful measures but never has it mandated Member States to recourse to force in collective self defence except in furtherance of the interpretation given to Resolution 678.


Terrorism is a serious threat to peace and security and must be dealt with rigorously and without delay. However, the struggle against terrorism must be confined to limits of law. The contention that the current norms of international law are insufficient to deal with the threat of terrorism is unconvincing. Currently, International Law provides for self-defence and anticipatory self-defence for any situation threatening peace and security. What is needed is to make the Security Council a reliable and effective body. The doctrine of pre-emption cannot fit into the current international legal system and it does not present compelling arguments for it to be accepted as new norm of international law.

Self-defence must as a right, reflect international realities and aspirations. International law provides States with the ‘inherent’ right to defend themselves, while making the exercise of that right subject to law. It is submitted that Secretary Webster’s formulation of these guiding principles when applied in context does just that. However, as we have seen, the law of self-defence is expanding in several ways:

Self-defence is deemed to be lawful not only in response to an armed attack that has already occurred but also in case of threat of attack, if real.

Anticipatory self-defence has been stretched to encompass latent threats in addition to danger of an imminent armed attack.

Consensus seems to be emerging on the lawfulness of anticipatory self-defence, provided that it is given a narrow interpretation. On the contrary, pre-emption has not gained currency within the international community.

Origin of an armed attack may come not only from States but also from non-State entities to trigger the right of self-defence.

Self-defence against non-State entities has gained legal currency, even though not fully accepted by the ICJ.

States are stretching the duration of action in self-defence as may be clearly inferred by the US ‘war on terror’.

Given the prohibition on the use of force under the Charter, States are stretching the meaning of self-defence to justify the use of force and intervention for restoring peace and security. The relation between self-defence and necessity also requires clarification, because States often invoke the latter to infringe another States sovereignty when circumstances cannot allow it to rely on the right of self-defence. The plea of necessity cannot be invoked to circumvent the ‘imminence’ requirement under the doctrine of anticipatory self-defence. For an action under necessity is justified only if the danger is grave and imminent, as stated by article 25 of the ILC draft on State Responsibility. Rather, the plea of necessity might be a valid excuse for intervention if it is assumed that the State is ‘innocent’ and no wrongful act can be attributed to it.

In his ‘In Larger Freedom’ report, the Secretary General proposed that a draft resolution on the use of force be prepared by the Security Council, setting out principles for the lawful use of force under Article 51. Unfortunately, this recommendation was not endorsed by the World Summit in September 2005. What we can thus pessimistically conclude is that States do not favour a detailed definition of self-defence that limits their freedom of action and prefer to leave its boundaries undefined, so as to exploit opportunities given by this permissible use of armed force.