Trump’s Threat of Destruction of North Korea and Proportionate Defensive Force: An Assessment of Similar Observations in Legal Scholarship and US Practice

by Sina Etezazian

[Sina Etezazian serves as Digest of State Practice Regional Coordinator for the Journal on the Use of Force and International Law. He recently completed his PhD at Monash University. His doctoral thesis was titled “Ambiguities Regarding the Necessity and Proportionality Criteria for the Exercise of Self-Defense in International Law”. In 2017, he won the 2016 Monash Law School Students’ Publication Prize for his article providing a detailed reappraisal of proportionate self-defense].

On 19 September 2017, President Donald Trump stated in the UN General Assembly that if the US is “forced to defend itself or its allies, we will have no choice but to totally destroy North Korea”. This assertion appears to have constituted one of the most expansive positions the United States has taken during the UN era with regard to the scope of the right of self-defense in international law. The predominant academic view (see footnotes 84–5 and accompanying text) is that, like physical acts, individual statements that can be attributed to states may amount to evidence of state practice for the purpose of identifying and modifying a rule of customary international law. Trump’s threat of force against North Korea can thus be understood to provide evidence of US practice concerning the right of self-defense.

Of course, it is difficult to argue that Trump’s statement only applies to North Korea’s army. In contrast, this statement appears to extend to the whole country, including the North Korean civilian population, while it is clear that the law governing the use of force does not underpin such a broad reading of proportionate self-defense. However, Let us suppose for the sake of argument that President Trump only meant the destruction of North Korea’s army, rather than that of the whole country. This post clarifies why even this possible interpretation of Trump’s statement would run counter to the nature of the self-defense proportionality requirement.

It is worth emphasizing at the outset that – setting aside domestic criminal and constitutional law – the conduct of targeted killing and US officials’ legal arguments, as will be discussed in this post under the section “Drone strikes and non-compliance with proportionality since 2002”, implicate three distinct regimes in international law: international humanitarian law (IHL), international human rights law (IHRL) and international law on the use of force (the jus ad bellum regime) (see, for example, here, here, here, here, here, here, here, here, here, here, here, here, here, here, here, here, here and here. See also here and here). However, this post will focus only on the last; it does not entail a discussion of IHL and IHRL. Similarly, as this post aims to discuss the relevant practice exclusively in the context of the proportionality requirement, it does not address the content of the two other principal requirements for taking forcible self-defensive measures: “necessity” and “armed attack”. Nor does it aim to consider the concepts of “consent” and “intervention by invitation” and their applicability to the given situation.

Trump’s statement and Dinstein’s formula

Trump’s reliance on possible annihilation of North Korea’s army as being lawful defensive force, when examined through the lens of jus ad bellum proportionality, appears consonant with Yoram Dinstein’s observation that, in the event of a “war of self-defense”, the victim state not only is allowed to halt the large-scale attack that provoked the response but is permitted to engage in forceful measures to seek the “the destruction of the enemy’s army” (p 262). It is, however, noteworthy that Dinstein distinguishes small-scale armed attacks from an unlawful forcible action that prompted a “war of self-defense”. Accordingly, in relation to a minor forceful action, which typically occasions an “on-the-spot-reaction”, proportionality requires that the responding state must use force such that it causes harm only to the same degree as the initial attack. Yet, when a “war of self-defence” begins as a lawful response to an “all-out” aggression, Dinstein argues, the victim state is entitled to pursue the absolute military defeat of the attacker – that is, “the destruction of the enemy’s army”. This is because, in Dinstein’s view, there is no foundation in state practice for the idea that jus ad bellum proportionality continues to exist in a situation involving war, and that it has to be monitored constantly throughout the entire conflict. For this reason, Dinstein reiterates that, once a “war of self-defense” lawfully commences, given that a state is responding to a large-scale armed attack, that response need not be halted before the attacker is defeated except when the Security Council issues a binding resolution calling for the termination of hostilities (p 262). Dinstein’s characterisation of the destruction of the attacker’s army as being proportionate defensive force may thus be equated with Trump’s statement on 19 September 2017 with respect to the annihilation of North Korea’s army and the US’s right of individual and collective self-defense.

The nature of the self-defense proportionality requirement and Trump’s statement

As I have argued elsewhere, despite arguments to the contrary (see, for example, here p 235, 237, 240, 258, 262, 282; see also here), a detailed analysis of state practice concerning the self-defense proportionality requirement makes it possible to identify that states have mostly discussed this requirement in the context of the defensive aim of halting and repelling an attack. In other words, while in many instances of claimed self-defense actions, such as the 1964 UK aerial raid against Yemen, the 1965 US intervention in the Dominican Republic, Israel’s 1972 incursion of Lebanon and Russia’s 2008 action against Georgia, the reacting states have found the extent of the response and the level of casualties to be a relevant factor in measuring proportionality (see, for example, UN Doc S/PV.1108 (6 April 1964) pp 7–8, 10; “The Situation in the Dominican Republic”, Yearbook of the United Nations (1965) p 142; UN Doc S/PV.1644 (27/28 February 1972) p 19; UN Doc S/PV.1643 (26 February 1972) pp 3, 15; UN Doc S/PV.5953 (10 August 2008)), it appears that they have, to a certain degree, done so in the context of the purpose of halting the initial attack. This is demonstrated – at least to some extent – by the reaction of several states to the Israeli measures allegedly aimed at Hezbollah bases in Lebanon in 2006. Most of the states rejecting Israel’s assertion of self-defense highlighted the disproportionate nature of the action by reference to the extent of the harm inflicted on the infrastructure of the Lebanese state and the number of civilian victims. However, when the matter was addressed more thoroughly, it became clear that some states were underscoring the gravity of Israel’s action to argue that it had been disproportionate to the objective of self-defense, being the mere repelling of the initial attack (and possibly the impending attacks). Thus, the Russian representative expressed the view that “the scale of the use of force, the casualties and the destruction demonstrate that the actions stated for achieving this purpose go far beyond a counterterrorist operation” (UN Doc S/PV.5493 (Resumption 1) (21 July 2006)). Qatar took a similar stance, stating:

Everyone is fully aware of the grave situation in the Middle East; it has suddenly deteriorated as a result of the excessive use of military force by Israel against Lebanon on the pretext of self-defence. However, the greatest majority of the targets of the Israeli military aggression have been civilian targets, including the international airport, residential buildings, factories, power plants, bridges, highways and even grain silos and houses of worship. This leaves no doubt that the aim of this war goes beyond its stated objective (UN Doc S/PV.5493 (21 July 2006) 14).

Moreover, when reflecting on the definition of aggression during 1970–71, many states likewise clarified that jus ad bellum proportionality requires an action undertaken in self-defense to be weighed against the purpose sought by that action (See, for example, UN Doc A/AC. 134/SR. 67–78 (19 October 1970) pp 88, 89, 90, 89; UN Doc A/AC.134/SR. 79–91, (7 June 1971) pp 43–44). Similarly, Uganda, in the Armed Activities case in 2005, evaluated the proportionality of its response with respect to the objective of defense in the circumstances (Armed Activities on the Territory of the Congo (Democratic Republic of the Congo v Uganda) rejoinder submitted by the Republic of Uganda, pp 121, 124–25. See also ibid, memorial of the Democratic Republic of Congo, para 5.26; ibid, reply of the Democratic of Republic of Congo, para 3.159). It is worth noting that this position was shared by the states parties in the Oil Platforms case (Oil Platforms (Iran v US) counter-memorial submitted by the United States of America, p 141; ibid, rejoinder submitted by the United States of America, para 174–76), although Iran ultimately shifted to a more quantitative approach. Furthermore, in 2008, Panama employed the same reasoning when contending that Russia’s response against Georgia was “disproportionate” to what had been stated as the legitimate aim of self-defense in the given case, namely “protecting Russian citizens” from the initial attack by Georgian troops (UN Doc S/PV.5953 (10 August 2008) p 15). It therefore appears that, based on an assessment of customary international law, a precise equivalence between the magnitude of the attack and the harm done is a not a necessary aspect of the proportionality criterion for defensive force. Nevertheless, a response that has brought about much greater loss and damage than the initial attack is unlikely to be viewed as proportionate self-defense, as it has clearly gone beyond the mere halting of the attack.

Returning to Trump’s threat of force against North Korea and his self-defense justification in the General Assembly, it thus seems clear that the overthrowing of the attacker’s regime or defeating its army would not constitute a proportionate response unless it could be demonstrated that, under the exceptional circumstances of the case, this was the only way to achieve the objective of halting the forceful activities that accounted for the necessity of defense. However, while the destruction of a state’s army might be proportionate to the aim of repelling a nuclear attack by that state, as Kevin Jon Heller observes, it is clear that Trump has threatened to destroy North Korea in response to “any attack” by this country against the US or its partner nations; any such possible forcible action by the US would clearly be disproportionate under the law governing self-defense.

Drone strikes and non-compliance with proportionality since 2002

President Trump explicitly clarified – at least concerning response to a possible attack by North Korea – that the US’s version of proportionate defensive action is predicated upon the notion of the destruction of the attacker’s army. An examination of its recent practice relating to the exercise of the right of self-defense against both states and non-state actors, however, reveals that the US has engaged in disproportionate forcible measures since 2002, when it initiated its first drone strikes beyond the Afghan combat zone.

This can be seen – at least in part – from the position taken by then-Legal Advisor for the US Department of State Harold Koh, who claimed in 2010 that the United States was permitted to carry out drone attacks outside Afghanistan because it was still involved in self-defense operations against the al-Qaeda and Taliban groups in a continuation of Operation Enduring Freedom, which had begun on 7 October 2001. In a similar vein, then-Deputy National Security Advisor for Homeland Security and Counterterrorism John Brennan argued in 2012 that because the United States is engaged in an armed conflict with al-Qaeda, “it takes the legal position that – in accordance with international law – we have the authority to take action against al-Qa’ida and its associated forces without doing a separate self-defense analysis each time”.

However, the US managed to overthrow the Taliban regime and install an interim government, soon after it claimed defensive force in October 2001 to intervene in Afghanistan. Thus, even assuming that the removal of the Taliban government of Afghanistan could be regarded as proportionate self-defense, because it was necessary to effectively respond to al-Qaeda (for support of this view, see Lindsay Moir, Reappraising the Resort to Force: International Law, Jus ad Bellum and the War on Terror (Hart Publishing, 2010)), the aim of the defensive action had been achieved in the circumstances; this suggests that a separate series of unilateral forcible measures at least against the Taliban had required a separate justification based on Article 51 of the UN Charter. Despite this, the United States has extended its self-defense operations against the Taliban militants based in Pakistan since 2004, without providing a renewed self-defense assertion. It has continued to do so under the Trump administration.

Like Trump’s threat of force against North Korea, Koh’s and Brennan’s reasoning would appear to be based upon Dinstein’s formula of a “war of self-defense”, which maintains that “[t]here is no support in the practice of States for the notion that proportionality remains relevant – and has to be constantly assessed – throughout the hostilities in the course of war”. (For a similar viewpoint concerning John Brennan’s argument and its resemblance to Dinstein’s theory of the “war of self-defense”, see Kevin Jon Heller, “The Use and Abuse of Analogy in International Humanitarian Law” in Jens D Ohlin (ed), Theoretical Boundaries of Armed Conflict & Human Rights (Cambridge University Press, 2016) pp 252–4.) As regards the proportionality requirement in the exercise of self-defense, Trump’s statement cannot therefore be regarded as a total departure from the manner in which the US has invoked Article 51 to explain its drone strikes targeting alleged terrorists outside Afghanistan.


Trump’s reference to the possible destruction of North Korea’s army as permissible defensive action, coupled with the self-defense justifications advanced for the US’s wide-scale extraterritorial drone program since 2010, may reflect serious attempts to reinterpret and loosen the well-accepted rules on the principle of proportionality to the point of irrelevance. These expansive readings of self-defense, however, have never been endorsed by the rest of the international community or even the majority of them. On the contrary, the requirement of halting and repelling an armed attack still represents the only primary benchmark for the application of jus ad bellum proportionality. As noted above, this position is underpinned by an extensive reexamination of customary international law concerning proportionate defensive force, and such a reexamination provides a convincing rebuttal to the doctrine of a “war of self-defense”.

One Response

  1. Dear Sina,

    You correctly point out that most authorities agree that “statements that can be attributed to states may amount to evidence of state practice for the purpose of identifying and modifying a rule of customary international law.” However, you don’t mention that in order to identify customary international law, an element of opinio juris is required, i.e. the belief by the State that the practice in question is rendered obligatory by the existence of a rule of law requiring it. Personally, I highly doubt that Mr. Trump has much of a grasp on international law, and he surely says many crazy things on a regular basis. Given these considerations, to what extent do you believe that his statements at the UN truly reflect the opinio juris of his Administration?


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