INTRODUCTION
The right of self-defence is conferred on States by treaty and customary international law.[1] International treaty and customary law impose several restrictions on the exercise of this right. Self-defence is limited to those circumstances in which an ‘armed attack’ occurs[2] and defensive actions must not go beyond what is necessary and proportionate to repel an armed attack.[3] Where there is an ‘armed attack’ on a State, the instances of self-defence must be reported to the Security Council (SC) of the United Nations (UN)[4] and the right of self-defence is suspended as soon as the SC adopts measures necessary to maintain international peace and security.[5] This means that the Charter of the United Nations prohibits the use of force against another state except where the Security Council has authorised the use of force to maintain or restore international peace and security and also where a State is exercising its inherent right of individual or collective self-defence recognised by Article 51 of the Charter.[6]
States ordinarily rely on the right of self-defence to justify measures that would otherwise contravene the prohibition on the threat or use of force under Article 2(4) UN Charter and customary law.[7] Measures, in this context, are forcible where they involve the threat or use of violence[8], that means, they cause or threaten to cause ‘destruction to life and property’[9] States usually invoke the right of self-defence to justify forcible responses to armed attacks or violence. This right is subject to an additional restriction as it can only be engaged when States threaten or use force to resist an armed attack. In this way, the right of self-defence is presented as an exception to the principle of non-use of force.
Economic sanctions, security barriers and cyber operations are unlikely to amount to the use of force given that they do not usually cause death, injury, destruction or damage to people or property. Yet importantly, they may run into conflict with other rules of international law such as the principles of territorial sovereignty and non-intervention or, regarding economic sanctions, they may breach international trade, economic or investment law. If States have an ‘inherent right’to defend themselves against armed attacks as stated under Article 51 UN Charter, the question arises as to how such non-forcible measures can be justified under international law.
- SELF-DEFENCE AS COUNTER-FORCE[10]
In 2002 Israel built a security wall within occupied Palestinian territory to protect its population from terrorist attacks.[11] While other members of the international community alleged that the construction of the wall breached international human rights law and international humanitarian law,[12]Israel justified its action as an act of self-defence under Article 51 UN Charter.[13] In December 2003, the UN General Assembly (GA) requested an Advisory Opinion from the International Court of Justice (ICJ) on the legal consequences arising from Israel’s construction of the wall.[14]
In its Advisory Opinion to the GA, the ICJ found that the construction and permanence of the wall breached international human rights law and international humanitarian law.[15] Moreover, the Court rejected Israel’s claim of self-defence on the grounds that, first, this right cannot be engaged against a non-State actor and, second, the author of the armed attack cannot be located within the victim’s State’s territory or territory under its occupation.[16] Having dismissed Israel’s claim to self-defence on these bases, the Court did not have to examine whether this right can be invoked to justify the use of non-forcible measures such as the building of a security wall. However, in her Separate Opinion, Judge Higgins turned her attention to this question and, in a brief but important passage, she explained: “I remain unconvinced that non-forcible measures (such as the building of a wall) fall within self-defence under Article 51 of the UN Charter as that provision is normally understood”.[17]
It is worthy of note that Judge Higgins did not provide any legal justification or cite any authority to substantiate her statement.
According to Roberto Ago, he argued that the right of self-defence operates as a secondary rule of international law so far as it precludes State responsibility for breaches of the non-use of force principle.[18] James Crawford argued in contrast that self-defence being so closely related to the prohibition on the threat or use of force and that he saw it as forming an integral part of the prohibition itself.[19] Crawford therefore argued that Articles 2(4) and 51 UN Chartermust be read together as a singular primary rule of international law such that States cannot threaten or use force in their international relations except in self-defence. According to this approach, “a State exercising its inherent right of self-defence as referred to in Article 51 of the Charter is not, even potentially, in breach of Article 2, paragraph 4”.[20]
Crawford’s view that self-defence under Article 51 UN Charter is an exceptional right intrinsic to the non-use of force principle was adopted by the International Law Commission (ILC) in its Commentary to Article 21 of the Articles on State Responsibility (ASR)[21] which explains that:
“Article 51 of the Charter of the United Nations preserves a State’s ‘inherent right’ of self-defence in the face of an armed attack and forms part of the definition of the obligation to refrain from the threat or use of force laid down in Art 2, paragraph 4.[22]
It is noteworthy that Article 21 ASR also governs the matter of self-defence, but it must not be confused with Article 51 UN Charter. Article 21 ASR is a secondary rule of international law and precludes State responsibility for ancillary or incidental violations of international law that occur because of defensive measures being taken under Article 51 UN Charter, such as breaches of the principles of territorial sovereignty and non-intervention, a treaty of amity, a trade treaty, etc.THE DOCTRINE OF SELF DEFENCE UNDER INTERNATIONAL LAW[23]
The right to self-defence can be relied on to justify all measures necessary to ward off an armed attack.
- THE ORIGIN OF SELF-DEFENCE
This is a duty of self-preservation of a State. Article 51 UN Charter describes self-defence as an ‘inherent right’ and, as the ICJ explained that this phrase refers to the ‘pre-existing customary international law’ basis of this doctrine.[24]
Within the provisions of Article 51, nothing impairs the inherent right of self-defence. The objective of this provision is to preserve the customary right of self-defence and push it forward into the Charter subject to certain modifications. Thus, to better understand the content of this right under contemporary international law, inquiry into the customary practice of the right of self-defence prior to the adoption of the UN Charter is essential.
Historically, the right of self-defence was part of the duty of self-preservation.[25] Self-preservation was a natural law duty that required States to take all measures necessary to preserve their essential interests: “the so called right of self-preservation was … the virtually unrestricted freedom it gives to a state to act contrary to any norm of International Law, if such action is deemed necessary for its own preservation”.[26]
States refined the duty of self-preservation during the nineteenth century. What emerged was a right of self-defence and, being a product of State practice and opinio juris, it was a legal right conferred by way of customary law.[27] Over time, States developed customary law and placed limits on when and how the right of self-defence could be exercised. A good example, by the mid-nineteenth century it was accepted that defensive action could not go beyond what was necessary and proportionate to avert the threat of harm or attack.[28] States did not restrict the right of self-defence to the use of forcible measures exclusively. As a review of State practice reveals, in pursuit of self-defence, States were free to take all measures necessary to protect themselves from harm irrespective of which rules of international law they breached.
During the nineteenth century, the United States (US) regularly conducted military operations in Mexico to prevent Native Americans conducting attacks within the US territory. In July 1836, suspecting that Native Americans in Texas (then part of Mexico) were planning raids within the US, the US sent troops into Mexico and occupied parts of its territory and justified this action on the basis of ‘the immutable principle of self-defence’.[29] Mexico’s Minister to the US concluded that the US’s invocation of self-defence was not warranted in the circumstances and determined that ‘the honour and rights of my Country are … greatly compromised by the violation of its territory and subsequent occupation by US forces”.[30] In response, the US explained thus : “The present inability of Mexico to restrain the Indians within her territory from hostile incursions upon the citizens of the United States, if they should once be engaged in hostility near the frontier, and the barbarous character of their warfare which respects neither the rights of nations nor of humanity, renders it imperative on the United States to adopt other means for the protection of their citizens. What those means should be, must depend upon the nature of the danger. Should that require the temporary occupation of posts beyond the frontier, the duty of self-preservation gives them the right to such occupation.”[31]
In December 1837, British forces entered US territory to destroy the Caroline, a steamer being used to ferry weapons and other supplies to rebel groups in Upper Canada who were revolting against British rule. British forces killed at least one American national and, subsequently, fired the steamer and set it sail over Niagara Falls. This incident precipitated a significant diplomatic fallout between the UK and US which, over several years, exchanged correspondence debating the legality of the former’s actions.
In 1867, the US extended its jurisdiction over the Bering Sea after it purchased Alaska from Russia. The US alleged that Canadian vessels were hunting seals that were migrating through the Bering Sea, which it saw as unlawfully interfering with the commercial rights of US companies as guaranteed by US law. In 1886, US authorities apprehended several Canadian vessels while they were hunting for seals. As Canada was under British rule at the time, it was the UK who protested the seizure of the vessels. After diplomatic efforts to resolve the dispute ended unsuccessfully, the UK and US signed a treaty of arbitration and a Tribunal was established to consider a number of issues, one of which was: “has the United States any right, and if so, what right of protection or property in the fur seals frequenting the islands of the United States in Bering Sea when such seals are found outside the ordinary three-mile limit that falls with a State’s territorial sea”[32]
As the above case studies illustrate, during the nineteenth century the right of self-defence was seen as a general right under customary law that could be asserted to justify any conduct irrespective of which rule of international law it breached, provided of course the defensive action was necessary to protect the essential interests of the State. The principle of non-use of force was grafted onto international law via customary and treaty law later.
- NON-FORCE MEASURES AS SELF-DEFENCE AND COUNTERMEASURES[33]
There have been arguments as regards where a State suffers an armed attack and responds with non-forcible measures that are prima facie unlawful, it must rely on the doctrine of countermeasures to shield itself from international legal responsibility. An example, Sicilianos rejects Bowett’s claim[34] that States can invoke the right of self-defence to justify the use of non-forcible measures such as economic sanctions:
“Ceci ne signifie aucunement toutefois que l’Etat victime d’une agression armée (ouses alliés) ne pourraient réagir cumulativement par la force et par des mesures économiques ou autres. Ces derniéres, si elles sont en soi illicites, seront justifiées autitre de contre-mesures”.[35]
Under general international law, countermeasures are otherwise unlawful acts that are exceptionally permitted on the basis that they are designed to induce wrongdoing States into law compliance.[36] It may seem appropriate to rely on the doctrine of countermeasures to preclude State responsibility for non-forcible responses to armed attacks given that such attacks will usually qualify as unlawful uses of force.[37] However, while the doctrines of countermeasures and self-defence may overlap so far as they can apply to the same set of circumstances,[38] countermeasures will rarely provide a suitable legal mechanism to address non-forcible responses to armed attacks.
THE AIMS AND OBJECTIVES OF COUNTERMEASURES AND SELF DEFENCE
The doctrines of countermeasures and self-defence describe different phenomena and serve different aims and objectives. Notwithstanding the global reach of the UN’s collective security regime, international law remains a de-centralized system and much of its enforcement lies in the hands of those who believe they have been wronged.[39]The doctrine of countermeasures is therefore a mechanism by which injured States can enforce compliance with international law and protect their legal rights.
Like countermeasures, self-defence is a form of self-help but, unlike countermeasures, self-defence is not a law enforcement mechanism. The purpose of self-defence is to enable States protect themselves from armed attacks and, as such, it evokes a war-like paradigm.[40] Consequently, it is conceptually erroneous to describe non-forcible responses to armed attacks as countermeasures. Instead, this type of reaction is more accurately characterized as an act of self-defence.
- PRINCIPLES OF INTERNATIONAL LAW ON SELF DEFENCE[41]
- The law on self-defence encompasses more than the right to use force in response to an ongoing attack.
Article 51 of the UN Charter preserves the right to use force in self-defence “if an armed attack occurs”, until the Council has taken the necessary measures. On one view, the right is confined to circumstances in which an actual armed attack has commenced.[42] But the view that States have a right to act in self-defence to avert the threat of an imminent attack often referred to as ‘anticipatory self-defence’[43] is widely, though not universally, accepted.[44] It is unrealistic in practice to suppose that self-defence must in all cases await an actual attack.
The requirements set out in the Caroline case[45] must be met in relation to a threatened attack. A threatened attack must be ‘imminent’, and this requirement rules out any claim to use force to prevent a threat emerging. Force may be used in self-defence only when it is necessary to do so, and the force used must be proportionate.
- Force may be used in self-defence only in relation to an ‘armed attack’ whether imminent or ongoing.
In Article 51, an armed attack includes not only an attack against the territory of the State, including its airspace and territorial sea, but also attacks directed against emanations of the State, such as its armed forces or embassies abroad. An armed attack may also include, in certain circumstances, attacks against private citizens abroad or civil ships and airliners.[46] An ‘armed attack’ therefore is an intentional intervention in or against another state without that state’s consent or subsequent acquiescence, which is not legally justified.
An armed attack involves the use of armed force and not mere economic damage. Economic damage, for example, by way of trade suspension, or by use of a computer virus designed to paralyse the financial operations of a state’s stock exchange or to disable the technology used to control water resources, may have a devastating impact on the victim State but the principles governing the right to use force in self-defence are confined to a military attack. A purely ‘economic’ attack might however give rise to the right of self-defence if it were the precursor to an imminent armed attack.
- Force may be used in self-defence only when this is necessary to bring an attack to an end, or to avert an imminent attack. There must be no practical alternative to the proposed use of force that is likely to be effective in ending or averting the attack.
The criterion of necessity is fundamental to the law of self-defence[47]. Force in self-defence may be used only when it is necessary to end or avert an attack. Thus, all peaceful means of ending or averting the attack must have been exhausted or be unavailable. As such there should be no practical non-military alternative to the proposed course of action that would be likely to be effective in averting the threat or bringing an end to an attack. Necessity is a threshold, and the criterion of imminence can be seen to be an aspect of it, since it requires that there be no time to pursue non-forcible measures with a reasonable chance of averting or stopping the attack.
Necessity is also a limit to the use of force in self-defence in that it restricts the response to the elimination of the attack and is thus linked to the criterion of proportionality. The defensive measure must be limited to what is necessary to avert the on-going attack or bring it to an end.
- A State may use force in self-defence against a threatened attack only if that attack is ‘imminent’.
The concept of ‘imminence’ reflects the Caroline formulation of ‘instant, overwhelming, leaving no choice of means, and no moment for deliberation’. In the context of contemporary threats, imminence cannot be construed by reference to a temporal criterion only but must reflect the wider circumstances of the threat. The criterion of imminence requires that it is believed that any further delay in countering the intended attack will result in the inability of the defending state effectively to defend itself against the attack. In this sense, necessity will determine imminence: it must be necessary to act before it is too late.
- Article 51 of the UN Charter is not confined to self-defence in response to attacks by States. The right of self-defence applies also to attacks by non-state actors.
There is no reason to limit a state’s right to protect itself to an attack by another State. The right of self-defence is a right to use force to avert an attack. The source of the attack, whether a state or a non-state actor, is irrelevant to the existence of the right. The ICJ Wall Advisory Opinion should not be read as suggesting that the use of force in self-defence is not permissible unless the armed attack is by a state.[48] There is nothing in the text of Article 51 to demand, or even to suggest, such a limitation.[49]
- The exercise of the right of self-defence must comply with the criterion of ‘proportionality’.
In the Caroline formulation, the principle of proportionality was stated to require “nothing unreasonable or excessive, since the act, justified by the necessity of self-defence, must be limited by that necessity, and kept clearly within it.”
The ICJ has confirmed that it is a well-established rule of customary international law that a use of force in self-defence must be “proportional to the armed attack and necessary to respond to it.” [50] This requires that the level of force used is not greater than that necessary to end the attack or remove the threat. As such it is another way of looking at the requirement of necessity.
CONCLUSION
Self-defence is a general right under international law and, as such, permits States to take all measures necessary to counter an armed attack regardless of whether they amount to a threat or use of force.
Countermeasures and self-defence are distinct legal doctrines as they are triggered by different events and subject to their own conditions and restrictions. Fundamentally, the reason why there are such significant differences between these doctrines lies in the fact that countermeasures are responses to illegality and thus law enforcement mechanisms whereas self-defence is a response to grave violence and attack and thus an act of self-preservation.
FOOTNOTES:
[1] See Article 51 UN Charter and Case Concerning Military and Paramilitary Activities in and against Nicaragua
(Nicaragua v. United States of America), Judgment (Merits) [1986] ICJ Rep. 14, para 176.
[2] Article 51 UN Charter.
[3] Nicaragua (n 1) para 176; Legality of the Threat or Use of nuclear weapons, Advisory Opinion [1996] ICJ
Rep. 226, para 41; Case Concerning Oil Platforms (Islamic Republic of Iran v. United States of America),
Judgment (Merits) [2003] ICJ Rep. 161, para 76.
[4] Article 51 UN Charter.
[5] Article 51 UN Charter.
[6] Article 51 UN Charter.
[7] Nicaragua (n 1) paragraph 34 (confirms that the principle of non-use of force is established in customary law).
[8] Y Dinstein, War, Aggression and Self-Defence (CUP 2017) 90.
[9] I Brownlie, International Law and the Use of Force by States (OUP 1963) 362
[10] Buchan, R. (2023) Non-forcible measures and the law of self-defence. International and Comparative Law Quarterly, 72 (1). pp. 1-33. ISSN 0020-5893 https://doi.org/10.1017/s0020589322000471
[11] For an overview of Israel’s construction of the wall see Report of the Secretary-General Prepared Pursuant to
General Assembly Resolution ES-10/13, UN Doc. A/ES-10/248 (November 24, 2003).
[12] UNGA A/ES-10/PV.21 (October 20, 2003).
[13] ibid 5-8 (remarks of the Israeli representative to the UN).
[14] UNGA Res. ES-10/14 (December 8, 2003)
[15] Legal Consequences of the Construction of a Wall in the Occupied Palestinian Territory, Advisory Opinion
[2004] ICJ Rep. 136, para 137.
[16] Legal Consequences of the Construction of a Wall in the Occupied Palestinian Territory, Advisory Opinion
[2004] ICJ Rep. 136, para 137.
[17] ibid para 35 (Separate Opinion of Judge Higgins).
[18] ‘The State finds itself in a position of self-defence when it is confronted by an armed attack against itself in
breach of international law. It is by reason of such a situation that, in a particular case, the State is exonerated from the duty to respect, vis-à-vis the aggressor, the general obligation to refrain from the use of
force’; International Law Commission, Eighth Report on State Responsibility by Mr Roberto Ago, Special
Rapporteur – The Internationally Wrongful Act of the State, Source of International Responsibility (Part 1), UN Doc. A/CN.4/318/Add.5-7 (1980) para 87.
[19] International Law Commission, Second Report on State Responsibility by Mr James Crawford, UN Doc.
A/CN.4/498 and Add 1-4 (1999) para-298.
[20] ibid.
[21] The UN General Assembly has on several occasions commended the ILC’s ASR to UN member States. UNGA Res. 56/83 (2001); UNGA Res. 59/35 (2004); UNGA Res. 62/61 (2007); and UNGA Res. 65/19 (2010)
[22] International Law Commission, Articles on State Responsibility for Internationally Wrongful Acts, with
Commentaries (2001) Commentary to Art. 21, para 1.
[23] Buchan, R. (2023) Non-forcible measures and the law of self-defence. International and Comparative Law Quarterly, 72 (1). pp. 1-33. ISSN 0020-5893 https://doi.org/10.1017/s0020589322000471
[24] Nicaragua (n 1) para 176.
[25] M Roscini, ‘On the ‘Inherent’ Character of the Right of States to Self-Defence’ (2016) 4 Cambridge Journal
of International and Comparative Law 634.
[26] H Kelsen, Principles of International Law (Rinehart and Co. 1952) 59. ‘In the last resort almost the whole of
the duties of states are subordinated to the right of self-preservation’; WE Hall, A Treatise on International Law
(Clarendon Press 1884) 244. ‘From the earliest time of the existence of the Law of Nations self-preservation
was considered sufficient justification for many acts of a State which violate other States’, L Oppenheim,
International Law: A Treatise, Vol. 1 (Peace) (Longmans, Green & Co. 1912) 184.
[27] RY Jennings, ‘The Caroline and McLeod Cases’ (1938) 32 AJIL 82.
[28] The Caroline incident in 1837 – discussed in detail below – is often seen as subjecting the right of self–defence to the principles of necessity and proportionality.
[29] John Forsyth, Secretary of State of the United States, to Powhatan Ellis, Unites States Chargé d’Affairs at
Mexico City, December 10, 1836’ in WR Manning (ed), Diplomatic Correspondence of the United States:
Inter-American Affairs 1831–1860 (1937) Vol. 8 (Mexico 1831–1848 (Mid-Year)) 73.
[30] ‘Manuel Eduardo de Gorostiza, Mexican Minister to the United States, to Asbury Dickens, Acting Secretary
of State of the United States, October 10, 1836’, ibid 367
[31] Asbury Dickins, Acting Secretary of State of the United States, to Manuel Eduardo de Gorostiza, Mexican
Minister to the United States, October 13, 1836’, ibid 67
[32] Fur Seals Arbitration (1893) 1 Moore Arbitrations 755, 906.
[33] Buchan, R. (2023) Non-forcible measures and the law of self-defence. International and Comparative Law Quarterly, 72 (1). pp. 1-33. ISSN 0020-5893 https://doi.org/10.1017/s0020589322000471
[34] See e.g., DW Bowett, Self-Defence in International Law (MUP 1959) 270 (and, later, DW Bowett, ‘Economic Coercion and Reprisals by States’ (1972) 13 Virginia Journal of International Law 1, 7); CJ Tams, ‘Light Treatment of a Complex Problem: The Law of Self-Defence in the Wall Case’ (2006) 16 EJIL 975, footnote 75; Solon Solomon, ‘Legitimate Non-Forcible Measures of Self-Defence: The Post-Disengagement Israeli Measures towards Gaza as a Case Study’ (2010) 9 Chinese Journal of International Law 501
[35] Sicilianos (n 24) 295 (‘This does not mean, however, that the State that is the victim of armed aggression (or its allies) could not react cumulatively by force and by economic or other measures. The latter if they are in themselves unlawful, will be justified as countermeasures’ (author’s translation)). ‘The key feature of the right of self-defence by states is using significant armed force against another state, beyond the defender’s own territory. Defensive action not involving significant force is better referred to by other terms, such as intervention, retorsion, and countermeasures’; ME O’Connell, The Art of International Law in the International Community (CUP 2019) 158. ‘If these measures [non-forcible acts of self-defence] involve a breach of the acting State’s international obligations then, prima facie, they must purport to be countermeasures’; Scobbie (n 25) 1129. See also Paddeu (n 23) 113.
[36] As the ILC explains, a State can engage in ‘countermeasures against a State which is responsible for an internationally wrongful act to induce that State to comply with its obligations’; ASR (n 21) Art. 49(1).
[37] T Ruys, ‘Armed Attack’ and Article 51 of the United Nations Charter: Evolutions in Customary International Law and Practice (CUP 2010) 162; H Kelsen, ‘Unrecht und Unrechtsfragen in Völkerrecht’ (1932) 12 Osterreichische Zeitschrift fur Offentliches Recht 481
[38] Tams (n 69) 215-6
[39] Countermeasures are a feature of a decentralized system by which injured States may seek to vindicate their rights and to restore the legal relationship with the responsible State which has been ruptured by the internationally wrongful act’; ASR (n 21) Commentary to Chapter II, para 1.
[40] There is, in existing law, a clear distinction to be drawn between two forms of self-help. One, which is of a retributive or punitive nature, is termed ‘retaliation’ or ‘reprisal’ [or a countermeasure]; the other, which is expressly contemplated and authorized by the Charter, is self-defence against armed attack’; United Kingdom (1964) cited in Bowett, ‘Economic Coercion and Reprisals by States’ (n 26) 8. ‘countermeasures are also distinct from the notion of self-defence … [T]heir purposes are different: countermeasures are a law enforcement tool, whereas self-defence is a defensive reaction designed to restore a certain military balance vis- à-vis an attacking State’; Dawidowicz (n 73) 20. ‘[T]here is undeniably a common element, in that in both cases [of countermeasures and self-defence] the State acts after having suffered an international wrong, namely, the non-respect of one of its rights by the State against which the action in question is directed or at least in the face of such a danger. But any possible resemblance or true analogy stops at this point … “Self- defence” and “sanction” are reactions relevant to different moments and, above all, are distinct in logic’; Eighth Report (n 17) paras 89-90
[41] Principles of International Law on the use of Force by States in Self Defence- Elizabeth Wilmshurst (2005) Chatham House.
[42] The International Court of Justice (ICJ) expressly left open the issue of the lawfulness of a response to the threat of an imminent armed attack in the Case concerning Military and Paramilitary Activities in and against Nicaragua (Nicaragua v USA) (Merits, 1986 ICJ Rep. 14, at para. 194). When the question of the existence of an armed attack featured in the Court’s overall reasoning on the law of self-defence, it appeared before the treatment of the principles of necessity and proportionality. The same framework was followed by the Court some 17 years later in the Oil Platforms Case (Case Concerning Oil Platforms (Islamic Republic of Iran v. United States of America, 2003 ICJ Rep.) where it first investigated the existence of an armed attack (paras. 61 to 64 and 72) before it turned to the application of the principles of necessity and proportionality (paras. 73 and 74).
[43] For the purposes of this document the term ‘anticipatory ‘self-defence is preferred over ‘pre-emptive’ self-defence, although the latter is also in current use, for example in the report of the United Nations Secretary-General’s High-level Panel on Threats, Challenges and Change: ‘A More Secure World: Our Shared Responsibility’ para.189.
[44] The United Nations Secretary-General’s response “In Larger Freedom” to the high-level panel report mentioned above states: “Imminent threats are fully covered by Article 51, which safeguards the inherent right of sovereign states to defend themselves against armed attack. Lawyers have long recognised that this covers an imminent attack as well as one that has already happened” (at para. 124). In the resolution adopting the World Summit Outcome the UN General Assembly reaffirmed that “the relevant provisions of the Charter are sufficient to address the full range of threats to international peace and security” and reaffirmed “the authority of the Security Council to mandate coercive action to maintain and restore international peace and security” but did not comment on the meaning of Article 51.
[45] The exchange between the US and the UK agreed that there be “a necessity of self-defence, instant, overwhelming, leaving no choice of means and no moment for deliberation” and the use of force, “justified by the necessity of self-defence, must be limited by that necessity, and kept clearly within it”.
[46] This does not, however, deal with the rescue of citizens abroad, which raises different issues.
[47] The criterion of ‘necessity’ if force is legally to be used in self-defence can be traced back to the language of the Carolineformula:
“it will be for … [Her Majesty’s] Government to show a necessity of self-defence, instant, overwhelming, leaving no choice of means, and no moment of deliberation” and the action must not be “unreasonable or excessive, since the act, justified by the necessity of self-defence, must be limited by that necessity, and kept clearly within it.”
The ICJ held in the Nicaragua case that “the specific rule whereby self-defence would warrant only measures which are proportional to the armed attack and necessary to respond to it” was “a rule well established under customary international law”, and re-affirmed this in its Advisory Opinion on the Legality of the Threat or Use of Nuclear Weapons (1996 ICJ Rep. 226)
[48] Note 11, at para. 139: “Article 51 of the Charter thus recognizes the existence of an inherent right of self-defence in the case of armed attack by one State against another State.” But the European Union statement made upon the adoption of General Assembly resolution ES-10/18 (concerning the Wall Advisory Opinion) suggests that EU member states and the other states associated with the statement would not accept the possible implication of the Opinion that self-defence is not available unless the armed attack is by a state. “The European Union will not conceal the fact that reservations exist on certain paragraphs of the Court’s advisory opinion .We recognise Israel’s security concerns and its right to act in self-defence.” The matter came up again in a recent case in the ICJ; the Court stated that in the absence of attribution of the armed force to a State there is no right of self-defence against that State. (Case concerning Armed Activities on the territory of the Congo (Democratic Republic of the Congo v. Uganda) (Merits, 2005 ICJ Rep., at paras. 146,147)). In line with the Wall Advisory Opinion this should not be read as prohibiting action in self-defence against non-state actors as such.
[49] While certain writers have argued that Article 51 concerns only responses to aggression against another state, their argument based on the French text is not persuasive. True, the French text of Article 51 uses the term aggression armée, and aggression is also the term used in Article 39, but the French Government accepted during the debates on the definition of aggression that aggression in Article 39 was not the same concept as aggression armée in Article 51; further, the English, Chinese and Spanish texts of the Charter use different terms for Articles 39 and 51.
[50] Nicaragua case, para.176; see also, para.41 of the Advisory Opinion on the Legality of the Threat or Use of Nuclear Weapons.
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