Next week, Donald Trump will become President of the United States. Again. Even before his assumption of the presidency, he seems to have started setting his country’s foreign policy. Among the many items on his agenda, we have witnessed all these ideas and proposals about making Canada the 51st state, seizing the Panama Canal and annexing Greenland, willingly or not. Thus, at a recent press conference, when asked by a reporter whether he could assure the world he would not use military or economic coercion as he tries to gain control of the Panama Canal and Greenland, Trump said, “No, I can’t assure you on either of those two. But I can say this, we need them for economic security.” He further added that he could impose “very high” tariffs on Denmark if it refused to sell Greenland to the United States.
Nobody knows what the next four years will be like – as that famous quote goes, it is difficult to make predictions, especially about the future. But there are some exceptions. We know that the four Trump years will be very anxious. And very orange. And that we will keep asking ourselves questions like – is he being serious? And is that legal? So, assuming that Trump’s recent comments foreshadow the policies that his administration will pursue from next week onwards, that the United States government will start threatening its allies and making such demands of them, we can ask: is that legal? This is perhaps not the most important question – the wisdom of alienating one’s allies is certainly more consequential – but it is one for us as lawyers to answer.
There are various angles from which this question could be approached. Some are pretty obvious. Article 2(4) of the UN Charter prohibits not merely the use of force, but also threats of force. The acquisition of territory through force – conquest – is categorically prohibited. Transfers of territorial title against the wishes of the population of that territory could violate the right of peoples to self-determination. And tariffs might violate WTO law or regional trade treaties (a topic on which I’m not an expert).
There is one rule of international law, however, that fits particularly well with Trump is doing, or will be doing. This is the prohibition of intervention in the internal or external affairs of other states. As interpreted by the ICJ in Nicaragua – a restatement of the law repeatedly affirmed by many states as authoritative – that prohibition has two elements: (1) an interference with a state’s reserved domain, those ‘matters in which each State is permitted, by the principle of State sovereignty, to decide freely’, which is (2) coercive in character.
I’ve recently discussed how that concept of coercion should be understood in a piece in the AJIL (here), a brief summary of which can also be found here. The core of my argument in that piece is that coercion can be understood in two different, if complementary ways, which I call coercion-as-control and coercion-as-extortion. The former, which need not detain us here, refers to measures directly depriving a state of its ability to control its sovereign choices – for example, cyber operations that interfere with elections. The latter, however, precisely describes what Trump is now doing. Coercion-as-extortion is a composite of two, and sometimes three, acts: a demand, a threat, and a harm.
There is no doubt that Trump’s demands of America’s allies – Denmark and Panama in particular – relate to matters within the reserved domain of these states. Each state has the right to decide freely (subject to the right to self-determination) on the cession of sovereign title of parts of its own territory. Demanding of a state to sell or otherwise transfer their territory to another is undoubtedly an interference with that state’s internal and external affairs. In other words, this not a situation in which the demand would relate to matters on which the target state is not permitted to decide freely, because it is bound by international law to comply – as, for example, if the United States demanded of Russia to withdraw from Ukraine, or of Afghanistan to respect the rights of women in its territory. These latter demands do not interfere with the target’s internal or external affairs at all.
On its own, a demand is perfectly lawful, whether it interferes with another state’s reserved domain or not. It is perfectly lawful for Trump to ask Denmark to sell Greenland to the United States. It could be smart or not, politically provocative or not, but simply asking is legal by itself. A demand becomes coercive, and thus potentially unlawful, only if it is coupled with a threat of harm – do what we say, or else.
If, as the ICJ said in Nicaragua, coercion is the ‘very essence’ of prohibited intervention, then the threat is the very essence of coercion-as-extortion. Inflicting the harm itself is not essential. A state may intervene in the internal or external affairs of another through a demand and a threat alone, without necessarily following through with the harm if the demand is rejected – although it may of course do so. (For example, in the cyber context, the official positions of the African Union, Canada, Costa Rica, Iran, New Zealand and the UK refer to threats (of force or more generally) as forms of coercive intervention. No state has said that threats cannot constitute coercion. See also my AJIL piece, at 627-8). Imagine if, counterfactually, Ukraine had given in to Russian demands and threats before the full-scale invasion in February 2022 – we would still regard Ukraine as a victim of coercion, even if the invasion had not materialized.
The key question here is whether all threats of harm are coercive, or only some, and, if so, which ones. Is there, in other words, a threshold that the threatened or implemented harm needs to cross for it to constitute coercion? There are three possible approaches to this threshold issue (see my AJIL piece, at 633-40). First, that only harms that states specifically agree on count as coercion – but that minimalist approach runs against the whole idea of the generality of legal rules, and states have not endorsed it. Second, that only harms that are already illegal under some other rule of international law constitute coercion. Thus, threatening unlawful force is coercive. Or, so-called hostage diplomacy – arbitrarily detaining some innocent citizens of another state, and otherwise violating their human rights, in order to compel their state to do or not do something – is coercive. Or, economic measures that violate WTO law, or regional trade treaties, would cross the threshold of harm for coercion for the purpose of the non-intervention rule as well.
The third approach – which is to an extent complementary to the second – is to say that even lawful harms can become coercive, if their impact on the target state is sufficiently severe. Thus, a threatened or implemented economic measure that is legal on its own would become illegal, as prohibited intervention, if it is coupled with a demand that intrudes upon the victim state’s internal or external affairs. The prohibition of intervention would thus prohibit not only conduct that is prohibited already, under some other rule, but also conduct that would otherwise be lawful were it not for its purpose – compelling the victim to comply with an illegitimate demand.
This severity-based approach to coercion is to my mind conceptually coherent, even if it is less certain in its outcomes than the alternatives. I explain in my AJIL piece how domestic criminal law, in the context of extortion-type offences, often prohibits otherwise lawful threatened or implemented conduct, if it is coupled with illegitimate demands. (Thus, for instance, it would be lawful for the leader of a union to threaten their employer with industrial action in order to compel the employer to improve the pay or other benefits of their employees. But it would normally not be lawful for the union leader to make such a threat to compel the employer to give only that leader a pay rise or some other corrupt gain). To my mind, international lawyers have too often been stuck in the rigid dichotomy between (lawful) measures of retorsion and (presumptively unlawful) reprisals/countermeasures. It is entirely possible for the prohibition of intervention to cover otherwise lawful acts, including economic measures, depending on the reason for which such acts are done.
This is, in fact, the approach taken in the Anti-Coercion Instrument adopted in late 2023 by the European Union (Regulation (EU) 2023/2675 of the European Parliament and of the Council of 22 November 2023 on the protection of the Union and its Member States from economic coercion by third countries; see also here and here). That instrument enables the EU to use economic measures to respond to unlawful economic coercion – unlawful because it violates the prohibition of intervention – used against the Union or its member states. The ACI has a threefold purpose: expressive, deterrent and institutional. It expresses the EU’s position on various points of international law. It attempts to deter third states – and here the main targets are the US and China – from taking coercive measures against the EU and its members, by signalling how the EU could respond. And it creates processes and institutional mechanisms through which decisions on such responsive measures could be taken, which was necessary as a matter of EU law.
Indeed, it may be that the ACI’s first real test will be in how the EU chooses to respond to what the new Trump administration does. The ACI may turn out to be a dud, with the EU caving in, at least to an extent, to Trump’s coercion. Or, it may be – and perhaps that’s the best case scenario – that Trump waters downs his threats, that EU leaders manage to appease his ego without practically giving him much (certainly not Greenland), and that the whole thing is resolved diplomatically. Or, it could be that Trump enacts his tariffs and some other measures, and that the EU responds by using the ACI.
The ACI is explicit on two key points of international law: that (credible) threats alone can be coercive, and that the threatened or implemented harms need not be illegal, so long as they cross a severity threshold. Thus, under recital (15) of the Regulation’s preamble (see also the definition of coercion in Art. 2 thereof):
Coercion is prohibited and therefore a wrongful act under international law when a country deploys measures such as trade or investment restrictions in order to obtain from another country an action or inaction which that country is not obliged to perform under international law and which falls within its sovereignty, and when the coercion reaches a certain qualitative or quantitative threshold, depending both on the objectives pursued and the means used. The Commission and the Council should take into account qualitative and quantitative criteria that help in determining whether the third country interferes in the legitimate sovereign choices of the Union or a Member State and whether its action constitutes economic coercion which requires a Union response. Among those criteria, there should be elements that characterise, both qualitatively and quantitatively, notably the form, the effects and the aim of the measures which the third country is deploying. Applying those criteria would ensure that only economic coercion with a sufficiently serious impact or, where the economic coercion consists in a threat, that only a credible threat, falls under this Regulation. In addition, the Commission and the Council should examine closely whether the third country pursues a legitimate cause, because its objective is to uphold a concern that is internationally recognised, such as, among other things, the maintenance of international peace and security, the protection of human rights, the protection of the environment, or the fight against climate change. (emphasis added)
Again, we shall we what threats Trump makes, or what threatened harms he actually implements, once in office. Were he, for instance, to threaten or implement a 25% tariff on all Danish imports into the United States, it will be interesting to observe how EU institutions apply the ACI’s ‘qualitative and quantitative criteria.’ On the one hand, Trump’s demands regarding Greenland are wholly illegitimate – from a legal and moral perspective, there is no redeemable quality to them. On the other hand, the impact of such tariffs, while undeniably economically damaging on say Denmark, would be many orders of magnitude removed from that of comprehensive sanctions such as those deployed against Cuba, North Korea or Russia. Thus, if one took a very restrictive approach to severity, which would require harms that seriously disrupt the functioning of a society, Trump’s tariffs would likely not rise to that level. If, by contrast, the severity threshold is set much lower, the EU could take responsive measures under the ACI more frequently. We shall see – again, it could very well be that the instrument is never used.
Either way, it is important to underline that coercive measures do not have to work, in the sense of inducing a desired change in the behaviour of the victim state, to count as coercion for the purpose of the prohibition of intervention. That is, coercion that fails in its stated objectives is still coercion. In fact, this has also been the view of the United States; in the words of the general counsel of the US Department of Defense:
Requiring coercion to actually produce the desired effect could have paradoxical results. It may disadvantage States that are better able to deflect or endure coercive acts because their resilience would foreclose a determination of prohibited intervention. And it could reward States whose attempted intervention fails. It could also mean the same act, directed towards two different States, could be a prohibited intervention against one State but not the other, depending only on attributes of the target State, for example, whether a target State’s cyber defenses were advanced enough to withstand the act. Such an outcome could impede the ability of States with more robust and resilient defenses to call out violations and, if desired and appropriate, to respond lawfully with countermeasures or other tools of international law.
That is, the fact that Denmark or Panama will in all likelihood resist US demands to sell Greenland or the Canal – at least unless Trump crosses all legal and moral boundaries and actually uses force – does not mean that these states have not been coerced. Credible threats of force, or economic measures that cross an illegality or severity threshold, are still unlawful. They are unlawful even if Trump, the alleged ‘master negotiator,’ was in the final analysis merely bluffing. The same goes for any coercive measures that the US actually implements against its allies; to the extent that they interfere with these state’s internal or external affairs, they will violate the prohibition of intervention.
