The Art of the Steal: Does the EU’s Mutual Assistance Clause Protect Greenland?

[Dr Aurel Sari is a professor of public international law at the University of Exeter Law School]

On 6 January 2026, US President Donald Trump restated his longstanding desire to take control of Greenland, declaring that the US needs the autonomous Danish territory ‘right now’. On the same day, White House Deputy Chief of Staff Stephen Miller confirmed that it is the formal position of the US Government that Greenland should be part of the US. White House Press Secretary Karoline Leavitt added that President Trump and his team are discussing a range of options to acquire Greenland and in this context noted that ‘utilizing the US military is always an option at the commander-in-chief’s disposal’.

The Danish Government has categorically rejected any possibility of ceding or selling Greenland to the US on multiple occasions since 2019. Danish Prime Minister Mette Frederiksen has stated unequivocally that ‘Greenland belongs to the Greenlandic people’ and has urged Washington to ‘stop the threats’. The Greenlandic Government has likewise rejected any change of status. In a joint statement issued on 6 January 2026, seven European nations—Denmark, France, Germany, Italy, Poland, Spain and the United Kingdom—declared that security in the Arctic must be achieved ‘by upholding the principles of the UN Charter, including sovereignty, territorial integrity and the inviolability of borders’, stating that ‘it is for Denmark and Greenland, and them only, to decide on matters concerning Denmark and Greenland’.

In the light of the Trump Administration’s resolve to ‘reassert and enforce the Monroe Doctrine to restore American preeminence in the Western Hemisphere’, as demonstrated recently by its armed attack against Venezuela on 3 January 2026, the question arises as to whether Denmark could invoke Article 42(7) of the Treaty on European Union (TEU), the EU’s mutual assistance clause, should the US attempt to take Greenland by force. 

Competing views have been expressed in the past as to whether Article 42(7) TEU applies to Greenland. This post explores these positions to suggest that the legal position is not conclusively settled. However, even if Article 42(7) TEU should not extend to Greenland, this would not prevent European allies from assisting Denmark in the exercise of the inherent right of individual and collective self-defence should the US launch an armed attack against Greenland. The terms of the North Atlantic Treaty do not preclude such assistance. 

The Territorial Scope of Article 42(7) TEU

Greenland is subject to Danish sovereignty, as the Permanent Court of International Justice confirmed in 1933. In 1946, Denmark registered Greenland as a non-self-governing territory with the UN pursuant to Article 73 of the Charter. Greenland’s colonial status was rescinded through an amendment to the Danish Constitution in 1953 and the territory was integrated into the Kingdom of Denmark. In 1954, the UN General Assembly accepted Greenland’s new status and removed it from the list of non-self-governing territories. Under both domestic and international law, Greenland is therefore part of the territory of the Kingdom of Denmark. 

The US has recognized the sovereignty of the Kingdom of Denmark over Greenland. Should the US nevertheless launch an armed attack against Greenland, this could engage Article 42(7) TEU, which reads as follows:

If a Member State is the victim of armed aggression on its territory, the other Member States shall have towards it an obligation of aid and assistance by all the means in their power, in accordance with Article 51 of the United Nations Charter. This shall not prejudice the specific character of the security and defence policy of certain Member States.

Commitments and cooperation in this area shall remain consistent with commitments under the North Atlantic Treaty Organisation, which, for those States which are members of it, remains the foundation of their collective defence and the forum for its implementation.

The critical phrase for our purposes is ‘on its territory’. Since Greenland is part of the Kingdom of Denmark, an act of armed aggression against Greenland would make Denmark the victim of that aggression ‘on its territory’. However, following a referendum, Greenland withdrew from the European Economic Community in 1985 and transitioned to the status of an Overseas Country and Territory (OCT) associated with the Community. As an OCT, Greenland is not part of the EU, but it is not a third country either, since it is part of the territory of a Member State.

Whether or not the geographical scope of Article 42(7) TEU extends to Greenland therefore depends on whether the phrase ‘on its territory’ refers to the national territory of a Member State in its totality or whether it refers only to national territory that falls within the territorial scope of the EU Treaties.

Competing Views, Unsettled Law?

Several experts support a wide interpretation of the geographical scope of Article 42(7) TEU to cover the entire national territory of the Member States (e.g. here, here and here). Proponents of this approach point out that a literal reading of Article 42(7) TEU implies that OCTs fall within the territorial scope of the provision. Indeed, the wording of Article 42(7) TEU may be contrasted with the solidarity clause in Article 222 of the Treaty on the Functioning of the European Union (TFEU), which refers more narrowly to the ‘territory of the Union’. Article 42(7) TEU is based on Article V of the Modified Brussels Treaty of 1954, which provided for mutual assistance should one of the parties to that agreement become the ‘object of an armed attack in Europe’. The omission of this geographical limitation militates in favour of a wide interpretation of the scope of Article 42(7) TEU. It is worth noting that the European Commission’s Chief Spokesperson specifically confirmed, during a press briefing in January 2025, that Article 42(7) TEU does apply to Greenland.

Supporters of the restrictive approach suggest that Article 42(7) TEU must be read as referring to ‘EU territory’, meaning territories to which the Treaties apply and which are an integral part of the EU (e.g. here, here and here). This includes the metropolitan territories of the Member States and their outermost regions (ORs), but not OCTs, such as Greenland. 

Much of this debate overlooks the fact that the territorial scope of the Treaties is expressly defined in Article 52 TEU, which in its first paragraph declares that the Treaties apply to the Member States and in its second paragraph refers to Article 355 TFEU for further detail. In turn, Article 355(1) TFEU states that the Treaties apply to the ORs listed in that provision, while Article 355(2) TFEU provides that the special arrangements for association set out in Articles 198–204 TFEU apply OCTs, which includes Greenland. In other words, whereas the Treaties apply in full to ORs, only Articles 198–204 TFEU apply to OCTs. This is confirmed by the Court of Justice of the EU, which has consistently held, beginning with its decision in Leplat, that ‘failing express reference, the general provisions of the Treaty do not apply to the OCTs’. Since Article 42(7) TEU makes no express reference to OCTs, it follows that it is not applicable to OCTs, including Greenland.

However, other decisions of the Court of Justice call into question this conclusion. In Kaefer and Procacci, the Court held that the courts of an OCT may submit a request for a preliminary reference, rejecting the argument that a court located in an OCT is not a court or tribunal ‘of a Member State’ within the meaning of Article 267 TFEU. It is difficult to reconcile this decision with the principle established in Leplat: since Article 267 TFEU does not mention OCTs in express terms, it should follow that Article 267 TFEU and thus the preliminary reference procedure is not applicable to courts and tribunals based in OCTs at all. Still, the Court noted that the OCT court involved in Kaefer and Procacci was an overseas French court and decided that it therefore fell within the scope of Article 267 TFEU. This suggests that for the general provisions of the Treaties to apply to an OCT, it is not necessary that they refer to OCTs in express terms. A reference to the Member States or their constituent parts, such as their courts or tribunals, could suffice, as such a reference may include their OCTs. On this reasoning, Article 42(7) TEU is applicable to Greenland because the phrase ‘on its territory’ constitutes an express reference to OCTs forming part of a Member State’s national territory, just as the phrase ‘a court or tribunal of a Member State’ in Article 267 TFEU constitutes an express reference to courts and tribunals located in OCTs that are part of a Member State’s justice system, as held in Kaefer and Procacci.

Consistency with the North Atlantic Treaty

Assuming, for the sake of argument, that Article 42(7) TEU extends to Greenland, would it be consistent with Denmark’s commitments under the North Atlantic Treaty (NAT) to invoke this provision against the US? This matters, as commitments and cooperation under Article 42(7) TEU must remain consistent with commitments under NATO.

There are good reasons to believe that there would be no inconsistency. The North Atlantic Treaty does not curtail or otherwise limit the inherent right of self-defence of NATO members. This is confirmed by Article 7 NAT, which declares that the Treaty does not affect the rights and obligations of NATO members under the UN Charter, which includes their right of self-defence under Article 51 of the Charter. Accordingly, nothing in the NAT prevents Denmark and other NATO members from exercising the right of individual and collective self-defence against the US, whether they do so on an ad hoc basis or pursuant to Article 42(7) TEU. Moreover, NATO members have committed themselves in Article 1 NAT to refrain in their international relations from the threat or use of force in any manner inconsistent with the purposes of the UN and agreed in Article 2 NAT to contribute toward the further development of peaceful and friendly international relations between each other. Any use of force by the US against Greenland in violation of these commitments would surely constitute a material breach of the NAT within the meaning of Article 60 of the Vienna Convention on the Law of Treaties (VCLT), enabling Denmark and other parties to the NAT to rely on this breach as a ground for suspending the operation of the Treaty in whole or in part in the relations between themselves and the US. If there were any inconsistencies, these could be resolved.

Concluding Thoughts

The question whether or not Article 42(7) TEU applies to Greenland, and therefore whether Denmark may invoke this provision should the US commit an act of armed aggression against Greenland, is not settled. There are plausible arguments in support of both positions. 

However, the fact that Copenhagen may have a plausible legal argument for relying on Article 42(7) TEU may not be worth much. The Trump Administration’s embrace of a reinvigorated Monroe Doctrine creates a strategic dilemma for European nations: as the US increasingly backs away from the values and principles on which the Transatlantic Alliance was built, sustaining that Alliance becomes ever more difficult in the face of blatant violations of the rule of law, yet decoupling from the US and risking an acrimonious or even openly hostile relationship is not something that European nations can afford, given their relative military weakness and the wider geopolitical environment, including Russia’s ongoing aggression against Ukraine. Even if the applicability of Article 42(7) TEU to Greenland was beyond any doubt, it would be naïve for Denmark to take for granted that its European Allies would rush to its assistance against the US should it invoke the clause. This is all the more the case given that the applicability of Article 42(7) TEU to Greenland is in fact unsettled.  

No one is off the hook, though. An armed attack by the US against Greenland would unleash a torrent of legal questions. Many of these may be doctrinally interesting, but their real significance lies in their strategic implications. For example, could Denmark invoke Article 5 NAT against the US and would European allies be bound to assist Copenhagen? Could other parties to the NAT terminate the Treaty by unanimous agreement in the relations between themselves and the US pursuant to Article 60 VCLT? Should the US rely on forces or assets stationed in the territory of other allies in any armed attack on Greenland, must any of those States seeking to remain neutral in an ensuing international armed conflict between the US and Denmark take measures to prevent their territory from being used by the US as a base of belligerent operations? Would such States have to intern US forces present in their territory? How could this be reconciled with the terms of the NATO Status of Forces Agreement? These questions pose difficulties not just for European allies, but notably also for Canada.

Even without the US resorting to the use of military force against Greenland, significant damage has already been done. The Trump Administration’s actions are approaching the point at which they amount to coercive intervention into the affairs of Denmark and a threat to use of force. They may in fact have crossed those thresholds. At some point, European governments may have no choice but to confront the strategic dilemma they are facing head on.

Photo attribution: “Scenery from Ravnefjeldet, Nanortalik (Southernmost part of Greenland) on a clear December morning” by Jens Buurgaard Nielsen is licensed under CC BY-SA 3.0