By: Toby Fenton
With World War II underway, in August 1941, Britain and the USSR invaded Iran in an operation lasting several weeks. In June 1967, Israel launched an attack on Egypt, destroying most of the Egyptian air force and marking the start of the Six Day War. In March 2003 a US-led coalition invaded Iraq, with the ensuing Iraq War becoming a conflict whose end is still indeterminate. In all three cases, Britain/USSR, Israel and the USA claimed that they were acting in self-defence. However, in all three cases, these states used military force before an attack against them had taken place. And in the near future, states may well seek to deploy cyber-military force in a similar manner.
This article looks at the question of the legality of ‘anticipatory’ self-defence – the idea of using force in self-defence prior to being attacked. Beyond the cases mentioned above, the debate over this issue was invigorated greatly in the mid-20th century with the advent of nuclear weapons, and it has seen increased attention in our times with the evolution of new threats in the post-Cold War international security environment.
This article argues that the question of the legality of anticipatory self-defence has a relatively simple answer: the word ‘anticipatory’ is largely redundant, having little legal significance. Instead, the (un)lawfulness of the use of force under the rubric of ‘anticipatory self-defence’ remains dependent upon the particular facts of each case, namely whether the use of force fulfils the requirements of necessity and proportionality that condition the fundamental international law right of self-defence.
Interpreting Article 51 of the UN Charter
The right to self-defence is asserted in both treaty law and customary law. While Article 2(4) of the UN Charter prohibits the use of force in international relations, Article 51 recognises that all states have an ‘inherent right of individual or collective self-defence if an armed attack occurs’. The International Court of Justice (ICJ) has also confirmed that all states have an inherent customary right to self-defence. However, interpretations differ on the meaning of these provisions.
There are broadly two interpretive approaches to Article 51. The restrictive approach limits self-defence to instances of armed attack. Here, ‘alarming military preparations by a neighbouring state would justify a resort to the [UN] Security Council [UNSC], but would not justify resort to anticipatory force by the state which believed itself threatened’. Therefore, a ‘state can meet preparations for attack only by preparations to resist’. The expansive approach views self-defence as not limited to Article 51 conditions. In affirming its inherence, Article 51 leaves the right of self-defence in its customary form ‘as it existed prior to the [UN] Charter’. This suggests that the occurrence of armed attack is not the exclusive prerequisite to self-defence. Accordingly, anticipatory self-defence – in this instance understood therefore as action taken prior to armed attack – is an inherent right de jure.
Indeed, some writers suggest that precluding pre-attack self-defence would make a state ‘responsible for the restoration, instead of maintenance, of international peace and security’ – thereby contravening this primary UN Charter obligation. Other writers take the expansive approach even further, arguing that the ontological ‘self’ of the 21st- century state is intimately connected with the order and security of the international system so that a threat to this system is one against which a state may defend itself. However, this seems unreasonably permissive-without specifying the nature of the threat on a case-by-case basis, it is difficult to determine whether the operationalisation of this approach would meet the crucial legal requirements of necessity and proportionality.
The complexity of the debate around Article 51 is illustrated well by the Nicaragua case. Here, the ICJ noted a proper definition of armed attack ‘is not provided in the UN charter and is not part of treaty law.’ Nevertheless, the ICJ maintains that the right to self-defence ‘is subject to the State concerned having been the victim of an armed attack’ and does not apply in response to threats or uses of force not constituting armed attack. However, the ICJ also noted that self-defence is a customary right, existing alongside treaty law rather than being supervened by it – and that the UN Charter itself ‘does not go on to regulate directly all aspects’ of that right. In the absence of an armed attack, we can shed additional light on the conditions for the exercise of self-defence through reference to customary law.
Self-defence as customary right
The Caroline case arguably defined the traditional criteria for the customary law right to self-defence-necessity and proportionality. In 1842, U.S. Secretary of State Daniel Webster explained that the necessity of self-defence must be ‘instant, overwhelming, leaving no choice of means, and no moment of deliberation’. Regarding proportionality, self-defence 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’. As constituent norms of customary law, necessity and proportionality remain central to the exercise of self-defence, as confirmed by the ICJ  and the UN. Indeed, it is argued that necessity and proportionality are the only norms that remain ‘uncontested in the legal regime’.
However, while their existence may be uncontested, their application is less clear. Even if disaggregated along Websterian lines, it is difficult to determine when imminence-based necessity is factually present. This determination requires ‘assessments of intentions and conditions bearing upon the likelihood of attack or…of the likelihood that peaceful means may be effective to restore peace and remove the attackers’. A general lack of consensus remains as to when the threshold of necessity is reached in any particular instance. Proportionality is also problematic; a key issue is against what exactly self-defence must be proportional. For instance, in the Oil Platforms case, the ICJ emphasised the (dis)proportionality of the U.S. attack on the Salman and Nasr platforms not just in isolated relation to the Iranian attack to which it was said to be a response, but also in the context of the extensive and ultimately disproportionate U.S. ‘Operation Praying Mantis’ – of which the U.S.’ platform attack was only a part – against Iranian vessels and aircraft. To be lawful, self-defence actions must additionally be proportionate under the law of armed conflict and the principles of international humanitarian law. Yet there is a limit to how far these operational guidelines for the principles of necessity and proportionality can be delineated a priori, for ‘so much resides in the contingencies of a situation’.
While necessity and proportionality have often been discussed in relation to nuclear weapons, more recent technological developments pose further challenges. For instance, 21st-century conflict in cyberspace raises issues including attribution, asymmetry, and relative imperceptibility of attack preparation, while the real-world costs and impact of cyber attacks are hard to determine. Therefore, establishing the ‘imminence of the cyber attack and the necessity and proportionality of the reaction may prove to be an impossible task’, meaning anticipatory self-defence against cyber attack would be ‘extremely difficult to invoke in practice’. An implicit choice is to be made between literal interpretations of necessity and proportionality, and more ‘flexible’ interpretations that appreciate the particularities of cyberspace.
Applying the logic on the distinction between ‘war’ and ‘armed conflict’ to the present issue, it appears here that it is the factual concept of self-defence – including compliance with necessity and proportionality – not the technical concept of anticipatory self-defence, that would indicate lawfulness. This has significant implications for defence policy, particularly if anticipatory or even ‘pre-emptive’ force is deemed a doctrinal requirement against 21st-century threats. Indeed, the ICJ has indicated that the lawfulness of such a doctrine would depend on the lawfulness of the particularities of the force advocated within – a position echoed more recently by the U.K. Attorney-General. Moreover, the notion that legal guidelines (or lack thereof) are such that a would-be defending state might – with some influence of international community opinion – itself determine the nature of an attack and thus the necessity and proportionality of the response illustrates the nebulousness of self-defence as an international legal concept. It also reveals the potential for abuse through using notions like necessity and proportionality to discursively support ‘the morality of a particular use of force’.
Self-defence, peace, and security
The international legal concept of self-defence has been described as perhaps the most ‘potentially dangerous ground’ for invoking military action – and the concept of ‘anticipatory self-defence’ is no less problematic. From this article’s discussion, two possible scenarios emerge. First, actions conducted under the rubric of ‘anticipatory self-defence’ that exceed the constitutive criteria of self-defence would likely violate the treaty law provisions of Article 51 and the customary law right. Alternatively, actions that factually fulfil the constitutive criteria of self-defence would likely be consistent with Article 51 and customary law provisions; in this scenario, the term ‘anticipatory’ would be largely redundant. This position agrees with other writers who argue that semantic wordplay – including the use of terms like ‘anticipatory’ – is less legally (though not necessarily politically) significant than compliance with the constitutive criteria of self-defence. In both scenarios, it is the legal facts of the particular case that matter most.
Finally, this emphasises some key challenges for the international legal agenda: namely, to (re)affirm – and, if necessary, update – the concepts of ‘armed attack’, ‘necessity’, and ‘proportionality’ in order to clarify the constitutive character of self-defence and the conditions for exercising it in contemporary international society. Addressing this task may prove crucial to international peace, security, and stability in the 21st century.
Toby Fenton is currently pursuing a Master’s degree in International Peace & Security at King’s College London.
 Jessup, P. C., A Modern Law of Nations, vol. 1. (New York: Macmillan Co., 1948), pp.166-167
 Gow, J., Defending the West (Cambridge: Polity Press, 2005), pp.118-147
 ICJ, Military and Paramilitary Activities in and against Nicaragua (Nicaragua v. United States of America) (1986), p.14
 Jessup, p.166
 Erikson, p.136
 Van den hole, p.85
 Van den hole, p.86
 Gow, pp.118-147
 ICJ 1986, para.176
 ICJ 1986, para.195
 ICJ 1986, para.176
 Cited in Jennings, p.89
 Cited in Jennings, p.89
 ICJ 1986, para.176; ICJ, Legality of the Threat or Use of Nuclear Weapons. Advisory Opinion (1996), para.41
 Gardam, J., Necessity, Proportionality and the Use of Force by States. (Cambridge: Cambridge University Press, 2004), p.27
 Schachter, p.1635
 Gardam, p.26
 Shaw, p.1142
 ICJ, Oil Platforms (Islamic Republic of Iran v. United States of America) (2003), paras.76-77
 ICJ 1996, para.42
 O’Connell, D. P., The Influence of Law on Sea Power (Manchester: Manchester University Press, 1975), p.34
 See Goodman, W., ‘Cyber Deterrence: Tougher in Theory than in Practice?’, Strategic Studies Quarterly, 4(3) (2010); Junio, T. J., ‘How Probable is Cyber War? Bringing IR Theory Back in to the Cyber Conflict Debate’, The Journal of Strategic Studies, 36(1) (2013)
 Healey, J., A Fierce Domain: Conflict in Cyberspace, 1986 to 2012 (US: Cyber Conflict Studies Association, 2013), p.31
 Roscini, M., Cyber Operations and the Use of Force in International Law (Oxford: Oxford University Press, 2014), pp.79-80
 Roscini, p.80
 E.g. Gow
 ICJ 1996, para.47
 UK Attorney-General, ‘Attorney General’s Advice On The Iraq War: Resolution 1441’, International and Comparative Law Quarterly, 54(3) (2005), para.3
 Shaw, pp.1142-1143
 Gardam, p.20
 Jennings, p.82
 E.g. Shaw, p.1140
Image 1 source: http://www.telegraph.co.uk/news/2016/06/09/if-jeremy-corbyn-had-stopped-tony-blair-invading-iraq-dictators/
Image 3 source: http://cimsec.org/20754-2/20754