Symposium on Erin Pobjie’s Prohibited Force: Scoping out the Prohibition on the Use of Force in Anomalous Situations

[Andrew Clapham is Professor of International Law at the Geneva Graduate Institute and the author of “War”]

During Dr Pobjie’s book launch at the Geneva Academy we discussed some of the contemporary challenges facing those working to ensure respect for the international law on prohibited force. It is obvious that states are not willing to take the necessary steps to deal with violations of this rule when the violator is an ally or the aggressor is simply too dangerous. Many might give up at the point. The more complicated legal challenge is trying to delineate the contours of what sort of force is permitted in self-defence. I consider the correct interpretation of the rule prohibiting force demands that acts of self-defence have to be judged against what is proportionate in the circumstances at the time, rather than the idea that once an attack has occurred a state is entitled to use force until it has achieved some sort of victory. The need to take seriously the prohibition on unnecessary and disproportionate force in self-defence has never been more urgent. Self-defence has limits under contemporary international law.  As Adil Haque puts it “Under the law of self-defense, even a legitimate aim must be set aside if it is outweighed by the harmful effects of the force necessary to achieve it.”  

As is well known to readers of this blog-site there are attempts to infuse the law of self-defence with old ideas from the law of neutrality. The suggestion is that, where a state is unwilling or unable to deal with threats emanating from its territory, the law of self-defence would allow a state acting in self-defence (collective or individual) to use force against an armed non-state actor responsible for an attack beyond the host state. Such a connection between the modern law of self-defence and old rules on neutrality has been criticized, and this issue is not addressed head on by Dr Pobjie, and cannot be dealt with here; but my attention was caught by Dr Pobjie’s Chapter on ‘anomalous examples’ of the use force. Taking the general Assembly’s 1974 Definition of Aggression as a starting point she considers military occupation, a state allowing its territory to be used by another state for an act of aggression against a third state, the unauthorized use of armed force from within another state, and the blockade of ports or the coast of another state. I should like to concentrate on this last example, particularly the question of the use of force against neutral shipping on the high seas in the context of blockade. A similar reliance on pre-UN Charter law relating to neutrality can be discerned here.

Dr Pobjie separates out the law of neutrality and the jus in bello from the jus contra bellum and questions whether “whether the law of neutrality and these rights of blockade continue to apply in the post-Charter era” (at p. 166). The relevant passage (without the footnotes) reads:

a more interesting legal issue is raised when it comes to the enforcement of a blockade against a neutral merchant vessel on the high seas. 

Under the jus contra bellum, the enforcement of a blockade against a ship flagged to a neutral State may amount to a use of force within the meaning of article 2(4) and violate the prohibition of the use of force unless justified by one of the recognised exceptions, that is, self-defence. This view is supported by State practice, for example, the position taken by the UK during the Gulf War, when it claimed that Iran’s visit of a British-flagged merchant vessel on the high seas was justified as a measure of self-defence under article 51 of the UN Charter. This implies the legal view that stopping and searching a foreign-flagged merchant vessel on the high seas would otherwise constitute an unlawful use of force in violation of article 2(4) of the UN Charter – that is, that it would not be justified by the law of neutrality. It is not the blockade itself that transforms the capture or attack of the neutral ship into a use of force – due to the principle of exclusive flag State jurisdiction, such interference with a vessel flagged to a third State on the high seas takes place in ‘international relations’ and is arguably itself a use of force unless the capturing/attacking State has lawful grounds for the exercise of jurisdiction over the vessel, for example, under article 110 of the UN Convention on the Law of the Sea.

But under the laws of naval warfare (jus in bello), ‘since neutral merchant vessels and civilian aircraft are obliged to respect a blockade that conforms to the legal requirements of publicity and effectiveness they become liable to interception and capture if they act in violation of the legitimate right of the blockading power to prevent egress from, or ingress to, the blockaded area’. Under the jus in bello, neutral merchant vessels and civilian aircraft are liable to be attacked if they are clearly resisting interception and capture, because such an act leads to loss of civilian status and renders the vessel or aircraft a legitimate military objective. However, these rules apply under the laws of neutrality and armed conflict, not under the jus contra bellum. The law of blockade and jus in bello do not prohibit the attack, but neither do they justify it under the jus contra bellum. Therefore, attacking a merchant vessel attempting to resist intercept and capture by the blockading State in these circumstances would be an unlawful use of force unless justified by self-defence.

pp. 165-166

We are faced here with a real legal dilemma. In Dr Pobjie’s words we have now a “controversial question which remains open. On one view, belligerent rights and the traditional law of neutrality continue to exist in the post-Charter era, which means that the impairment of the rights of third States must be accepted. On another view, the law of neutrality was abolished by the UN Charter and either belligerent rights no longer exist, or they have continued in a modified form under the rubric of self-defence (p.165).” 

This all may seem very academic, but the lives of thousands of people depend on how we as international lawyers conceive blockade in the contemporary world. Consider the food insecurity in Africa that results from the interruption of grain exports from Ukraine and the food and other goods that need to arrive in Yemen and Gaza. Can it really be that the belligerent rights promoted by naval powers in the 19^th Century have survived the Charter’s prohibition on the use of force? The idea that ancient jus in bello wartime belligerent rights to attack neutral shipping breaching blockade, or seize and acquire enemy ships and goods under the law of prize should be awarded to aggressor states has been seen as absurd in a system that outlaws the use of force (at 62), and I would suggest the time has come to re-evaluate the situation. In fact Sassòli (8.8.9) has recently concluded that “there are powerful reasons for considering that many rules of the law of naval warfare …, which differ from the rules of land warfare, can no longer be invoked by an aggressor State and there are some arguments that they are no longer appropriate and necessary even for a state fighting in conformity with jus ad bellum.” p 446.

But Dr Pojie is right to highlight that there is still an open controversy over the extent that old belligerent rights continue despite the advances in international law designed to reduce violence and protect civilians. It is surprising that recent manuals continue to carve out unhumanitarian exceptions for naval warfare and belligerent rights for both sides for war at sea. In the 2023 Newport Manual we find that “there is no rule that a blockade is unlawful if it has an effect on the civilian population that is disproportionate to the military advantage gained from the blockade” at p. 122;  and a defence of the idea that both belligerent states can acquire property rights over enemy and goods as prize: “While they are in or over international waters, or in or over any belligerent territorial sea or internal waters, enemy merchant vessels and civilian aircraft and their cargos are lawful prize and may be captured”. At p. 163. The history of naval warfare tells us that considering that all merchant ships on the other side are part of the enemy war effort led to tens of thousands of deaths merchant crew in the two World Wars.  There is a danger that wars involving economic naval warfare are somehow considered unencumbered by established principles of distinction and proportionality designed to save civilian lives and protect their property.

I have the sense that Dr Pojie is similarly concerned that her conclusions over the scope of the prohibition of the use of force are incompatible with the rights which some consider flow from belligerent rights, in particular those related to the establishment of blockade. Leaving aside whether an aggressor state can rely on such rights, she questions “whether the very imposition of a blockade remains a lawful instrument even for a State acting in self-defence, since the principle of effectiveness requires that the blockading State enforce the blockade against neutral vessels resisting interception and capture – in other words, that the blockading State use force against the vessels of third States” at p. 167.

Let us assume the progressive position that an aggressor state cannot rely on belligerent rights of blockade and a state acting in self-defence has no right to enforce a blockade against neutral shipping beyond what would be allowed as proportionate and necessary, under the law of self defence (similar to the UK position on stopping and searching neutral vessels in the Iran Iraq conflict as explained by Pobjie above), are we simply here at the vanishing point of enforcement? States show no interest in holding other states to account for their excesses in applying blockades. But we should not give up so easily, there may be one recent development which warrants attention. 

National courts are starting, particularly in the contexts of Yemen and Gaza, to grapple with the international law on transfers of arms, ammunition and parts. Dr Pobjie has highlighted that the prohibition on the use of force operates beyond the familiar scenarios involving attack and defence. The prohibition could inter alia extend to the imposition of blockade involving force used against neutral shipping. Violation of such a prohibition would then involve a violation of Article 2(4) of the UN Charter. Arms transfers that assist in such a violation of the UN Charter can be considered violations of the transferring state’s international obligations. These violations of the law on the use of force would be relevant for the application of the criteria under the EU Common Position and Article 6(2) of the Arms Trade Treaty.

 Even if the Security Council and relevant UN members states are unwilling or unable to uphold the rule of law concerning the use of force, there is a chance that some national courts will prevent their executive branches from authorizing arms transfers to states that are violating and will continue to violate international law. This wider reading of the prohibition on the use of force is relevant for such decisions. 

Dr Pobjie eschews a listing of the elements that are necessary to determine a prohibited use of force, instead she convincingly argues throughout the book that the use of force in this context is a “type”. This type is “characterised 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” (at p. 229). The author has successfully ensured that the book is open-access, and this expertly researched and argued text is already sure to prove invaluable for decision makers at all levels, and perhaps, one might hope, also for those considering the legality of arms transfers to states that are, not only violating the laws of war and human rights, but also engaged in the prohibited use of force, a type of prohibition so expertly explained by Dr Pobjie.