Symposium on Erin Pobjie’s Prohibited Force: Review by Tomohiro Mikanagi

[Tomohiro Mikanagi is an Ambassador/Deputy-Permanent Representative of the Japanese Permanent Mission to the UN and Ambassador-at-Large for Cooperation on International Law. He is a Former Legal Advisor of the Japanese Ministry of Foreign Affairs and former visiting fellow of the Lauterpacht Centre for International Law, Cambridge.]

The following comments are made in the author’s personal capacity

According to Erin Pobjie, “a ’use of force’ is a type, characterized by a basket of elements which do not all have to be present and which must be weighed and balanced to determine whether the threshold for the definition is met and an act is an unlawful ‘use of force’ under article 2(4) of the UN Charter.” (p. 229) As such elements, she refers to ‘contextual elements’ and elements of ‘use of force.’ (pp. 229-230) 

This approach sounds familiar to me. In 2016, I translated statements made by the Japanese Government on issues relating to use of force in my contribution to the Japanese Digest of International Law in the Japanese Yearbook of International Law. A typical answer to a Diet (Parliament) question on the determination of the existence of an armed attack explains:

As for the question on how to determine the point of the initiation of an armed attack, specific means and modality of an armed attack may vary. It may take such forms as bombardment, missile attack, and cross-border invasions by armed forces. Therefore, it would be necessary to take into account overall circumstances including the international situation, intention, means and modality to determine the specific point of the initiation of an armed attack.

p. 363 (emphasis added)

The underlined part and Erin Pobjie’s ‘type theory’ seem to have similarities. ‘The international situation’ in this Diet answer corresponds to Erin Pobjie’s contextual elements, and ‘intention, means and modality’ correspond to her elements of ‘use of force’. These elements constitute ‘overall circumstances’ to be taken into account, which correspond to her ‘basket of elements.’ While this Diet answer concerns an armed attack and Erin Pobjie’s ‘type theory’ concerns use of force, according to the ICJ’s Nicaragua judgment (para. 191), an armed attack is “the most grave forms of the use of force”, and the approach taken in determining the existence of an armed attack naturally has similarity with the approach taken in determining what constitutes use of force prohibited under article 2(4) of the UN Charter. 

These similarities between Erin Pobjie’s proposed approach towards use of force and the traditional approach taken in our Diet answers on an armed attack make her basic approach understandable and agreeable for me. 

Possible Application to Acquisition of Territory by Force

Having said that, I have several observations on the contents of her book, which I hope will contribute to her future research. As quoted above, Erin Pobjie argues that “a ’use of force’ is a type, characterized by a basket of elements which do not all have to be present and which must be weighed and balanced to determine whether the threshold for the definition is met and an act is an unlawful ‘use of force’ under article 2(4) of the UN Charter.” In the following, first, I would like to briefly examine if this approach works in determining what constitutes acquisition of territory by force. The prohibition of acquisition of territory by force is, according to the 2004 Wall Advisory Opinion of the ICJ, a ‘corollary’ of the prohibition of use of force incorporated in the Charter (para. 87). There is ambiguity in the term of ‘corollary’. On the other hand, the ICJ’s 2024 Palestine Advisory Opinion did not make clear distinction between the prohibition of acquisition of territory by force and the prohibition under article 2(4) of the UN Charter (para. 179). I am aware of criticism about this approach, but the following comments are made with the assumption that there is, at least, significant overlap between the prohibition of acquisition of territory by force and the prohibition of use of force under article 2(4) of the UN charter. 

In the context of acquisition of territory by force, even activities without actually employing physical means nor producing physical effects can sometimes amount to unlawful attempts to acquire territory by force. Erin Pobjie seems to admit the possibility of such activities to be a prohibited use of force (p. 167). Issues relating to this kind of activities were raised by Judge Owada and Judge Robinson in their respective separate opinions on the ICJ’s 2015 judgment on Costa Rica v Nicaragua case, and Judge Robinson called it ‘non-violent’ use of force. Inspired by this ICJ case, I also examined this issue in my short ICLQ article in 2018. In the 2004 Wall Advisory Opinion, the ICJ said:

The Court considers that the construction of the wall and its associated regime create a “fait accompli” on the ground that could well become permanent, in which case, and notwithstanding the formal characterization of the wall by Israel, it would be tantamount to de facto annexation.

para. 121

Erin Pobjie’s ‘type theory’ refers to several contextual elements. According to this book, contextual elements include: “two or more States”, “international relations”, and “Against the territorial integrity or political independence of any state of in any other manner inconsistent with the Purposes of the United Nations” (pp. 229-230). Erin Pobjie elaborates on the element of ‘international relations’ and argues that use of force to reclaim disputed territory not within ‘de facto control’ and use of force ‘in violation of international demarcation lines’ are usually in ‘international relations’ and therefore fall within the scope of the article 2(4) (p. 100). In various UN documents relating to situations in the Middle East, the Green Line has been considered to be an ‘International demarcation line’ which, according to Erin Pobjie, indicates the contextual element of ‘international relations’ which is required for falling within the scope of article 2(4) of the UN Charter. In the 2024 Palestine Advisory Opinion, the ICJ referred to relevant Security Council and General Assembly resolutions (paras 176-177), and these resolutions, including Security council resolution 242, should also constitute an important contextual element.

As elements of ‘use of force’ which need to be weighed up to determine whether an act meets the threshold of the prohibited use of force, Erin Pobjie refers to physical force, direct physical effect, objective/target, gravity, coercive or hostile intent (pp. 229-230). The construction of the wall discussed in the Wall Advisory Opinion itself did not involve actual use of weapons, but the wall’s effect of creating ‘fait accompli’ tantamount to de facto annexation seems to have particular significance in determining whether its construction amounts to unlawful attempt to acquire territory by force. Paragraph 173 of the 2024 Palestine Advisory Opinion reads:

173. In light of the above, the Court is of the view that Israel’s policies and practices, including the maintenance and expansion of settlements, the construction of associated infrastructure, including the wall, the exploitation of natural resources, the proclamation of Jerusalem as Israel’s capital, the comprehensive application of Israeli domestic law in East Jerusalem and its extensive application in the West Bank, entrench Israel’s control of the Occupied Palestinian Territory, notably of East Jerusalem and of Area C of the West Bank. These policies and practices are designed to remain in place indefinitely and to create irreversible effects on the ground. Consequently, the Court considers that these policies and practices amount to annexation of large parts of the Occupied Palestinian Territory.

Erin Pobjie also refers to ‘a territory not within de facto control’ as a contextual element qualifying for the application of article 2(4) of the UN Charter. G7 Foreign Ministers’ Communiqué adopted on 18 April 2023 in Karuizawa, Japan, reads as follows: 

The prohibition on the acquisition of territory resulting from the threat or use of force, reaffirmed in the Friendly Relations Declaration of 1970, should be observed in good faith. We strongly oppose any unilateral attempts to change the peacefully established status of territories by force or coercion anywhere in the world. In this regard, sending regular or irregular forces to unilaterally annex a territory is prohibited.

emphasis added

According to this Communiqué, if a State deploys armed personnel to a territory not within its ‘de facto control’ and under another State’s peacefully established administration to acquire the territory, the deployment would be likely to amount to acquisition of territory by force. Japan mentioned this in its oral submission on the Palestine Advisory Opinion and the separate opinion of Judge Cleveland on the Palestine Advisory Opinion quoted this part (para. 29). The concept of peacefulness derives partly from the Eritrea-Ethiopia Claims Commission’s Partial Award on Jus ad Bellum: Ethiopia’s laims 1-8 (19 Dec 2005). In this report the Commission found that Eritrea violated article 2(4) of the UN Charter by attacking and occupying the town of Badme which was under ‘peaceful administration’ by Ethiopia at the time (paras 10-16). The Commission later found that Badme belonged to Eritrea, but the finding on the sovereignty did not affect the finding on the violation of the article 2(4). In the context of acquisition of territory by force, the existence of peacefully established administration over a territory seems to be an important contextual element to be taken into account. 

Response to a Threat Below the Threshold of an Armed Attack

Lastly, I would like to touch upon issues relating to possible response to a threat below the threshold of an armed attack. As Erin Pobjie rightly points out in the introductory part of her book, “The existing legal uncertainty over the interpretation of prohibited force is open to exploitation by States, in so-called grey zone operations, which are designed to take advantage of ambiguity in the law or to remain below legal thresholds for armed response.” (p. 7) This ambiguity about the law relating to the threat below the threshold of an armed attack is causing problems for States facing such threats. Erin Pobjie seems to be skeptical about whether there are cases where States are allowed to use force in responding to use of force below the threshold of an armed attack (p. 179). However, Tom Ruys, in his 2014 AJIL article “The Meaning of “Force” and the Boundaries of the Jus Ad Bellum: Are “Minimal” Uses of force excluded from UN Charter Article 2(4)?”, seems to have a different view on this matter. In his article, he quoted Ian Brownlie’s “International Law and the Use of Force by States”. In this book, Brownlie referred to “The Particular Problems of Self-Defense on the High Seas” and wrote: “(a) It seems clear that vessels on the open sea may use force proportionate to the threat offered to repel attack by other vessels, or by aircraft.” (p. 305) What Brownlie called use of force proportionate to the threat offered to repel attack by other vessels against vessels flying national flag seem to include use of force against the threat below the threshold of an armed attack. 

In this regard, I tend to agree with Brownlie and Ruys in accepting that in certain situations States are allowed to use proportionate and necessary force to repel the threat posed to national vessels on the high seas, even if the threat does not amount to an armed attack. My contribution to the Japanese Digest of International Law in the 2016 Japanese Yearbook of International Law also included Diet answers relating to this question. This kind of use of force seems to be implicitly accepted by States engaging in operations protecting merchant vessels on the high seas, including in the Red Sea. On 8 February 2024, the Council of the European Union adopted Council Decision (CFSP) 2024/583 on “a European Union maritime security operation to safeguard freedom of navigation in relation to the Red Sea crisis (EUNAVFOR ASPIDES).” Paragraph 8 of this decision reads: 

the operation should accompany vessels, provide maritime situational awareness and protect vessels against multi-domain attacks at sea. It should remain defensive in nature. Forces deployed for the operation should act in compliance with applicable international law, including customary international law, including self-defence where conditions are met, to defend against an imminent or ongoing attack on their own, or third-party, vessels. The operation should act in full compliance with UNCLOS.

emphasis added

This decision indicates the growing practical importance of issues relating to the use of force against threats below the threshold of an armed attack.