On 6 January 2026, European leaders including President Macron, Chancellor Merz, and Prime Ministers Meloni, Tusk, Sánchez, Starmer, and Frederiksen issued a joint declaration reaffirming that:

“Arctic security remains a key priority for Europe and is critical for international and transatlantic security.”

Far from mere diplomatic formality, the declaration marked the strongest expression of European solidarity with Denmark and Greenland to date, responding to President Trump’s escalating threat to annex Greenland. While the EU and its Member States have consistently signalled support since Trump’s inauguration in early 2025, Europe’s strategy so far has been cautious and may no longer be sufficient. The current situation will test whether European solidarity can evolve beyond rhetoric into a form of “defence solidarity”, ultimately requiring Member States to share military burdens in defence of both Greenlandic Union citizens and European sovereignty.

Greenlanders as Union citizens

Few truly appreciate how deeply the Arctic – and Greenlanders – are already integrated into Europe and EU Law. As Koen Lenaerts, President of the Court of Justice of the EU, emphasised in his keynote speech at the FIDE Congress in Katowice, Poland, in May 2025, the EU stretches from the Atlantic to the Black Sea, from the Arctic to the Mediterranean.

Greenland’s closest ties are with Denmark, which firmly anchors it within the European context. The starting point is that Greenland, Denmark, and the Faroe Islands share the same constitution as parts of the Kingdom of Denmark. When Denmark joined the European Communities in 1973, Greenland acceded as an integral part of Denmark. However, in 1985, Greenland transitioned to the status of an Overseas Country and Territory (OCT). The OCT designation refers to regions maintaining historical, social, cultural, and/or political ties to an EU Member State, without possessing sovereign status or international legal personality. This status means that Greenland remains connected to the EU and, explicitly or implicitly, subject to the applicability of certain EU Law.

Crucially, Greenlanders are Union citizens by virtue of being Danish citizens. Article 20(1) TFEU makes this explicit: “Every person holding the nationality of a Member State shall be a citizen of the Union.” This interpretation was confirmed by the Court of Justice already in the 2006 Eman and Sevinger judgment, holding that “persons who possess the nationality of a Member State and who reside in a territory classified as an OCT may rely on the rights conferred on citizens of the Union.”

The rights of Union citizens are not exhaustively listed in Article 20 TFEU. Following the recent 2025 Commission v Malta judgment, it is clear that Union citizenship carries exceptionally far-reaching implications. As the Court of Justice emphasised:

“Union citizenship is one of the principal concrete expressions of the solidarity that forms the very basis of the integration process and is an integral part of the identity of the European Union as a specific legal system, accepted by the Member States on a basis of reciprocity… Moreover, in accordance with the principle of sincere cooperation enshrined in Article 4(3) TEU, each Member State must refrain from any measure that could jeopardise the attainment of the Union’s objectives.”

Among these objectives, Article 3(1) TEU is particularly relevant in the present context:

“The Union’s aim is to promote peace, its values, and the well-being of its peoples.”

Notably, in 2021 the EU adopted a then new Arctic policy, committing to deeper engagement in the region to address geopolitical, environmental, economic, security, and social challenges, while collaborating internationally to seize emerging opportunities. This commitment was reinforced in 2024 when European Commission President Ursula von der Leyen visited both the Faroe Islands and Greenland. During her visit to Greenland, she inaugurated the EU Office in Nuuk, establishing a tangible European presence in Greenland and the wider Arctic. The Arctic policy also underscores Greenland’s extensive political and policy dialogue with the EU, its preferential trade arrangements for access to the EU market, and its position as one of the largest OCT recipients of EU support per capita, with €225 million allocated between 2021 and 2027 (see Arctic policy, p. 5). At the end of 2025, the Commission launched a call for evidence and public consultation on the future “EU Arctic policy”, which ironically, given the gravity of the current threat, is issued by the Directorate-General for Maritime Affairs and Fisheries.

Solidarity in EU law

As highlighted by Commission v Malta, solidarity more than ever constitutes a powerful principle within EU Law, particularly when combined with another foundational principle, that of loyal cooperation, and with the objectives and values underpinning the Union. Solidarity is no longer merely a political notion; it is increasingly evolving into a legally binding and operational principle.

EU Law provides an architectural design within which solidarity can be operationalised. This design encompasses diverse forms of solidarity, structured through principles and norms, whose scope and intensity are not static but evolve over time in response to changing circumstances and priorities. In simplified terms, solidarity within EU Law has so far manifested primarily in two general forms, which often coexist. Each reflects different “degrees of intensity” and can, in principle, be linked to the EU’s level of “maturity” in a given policy field with the implicit assumption that the EU may increasingly resemble the organisation and institutionalisation of solidarity found in complex national societies.

The first manifestation of solidarity is characterised by minimal binding commitments, focusing primarily on cooperation and harmonisation. In essence, this form of solidarity reflects the most common type of EU action aimed at deepening integration. Crucially, it does not involve significant resource transfers or burden-sharing. While solidarity is present, it remains associated with a relatively low level of obligations.

The second manifestation of solidarity involves a higher level of obligations and requires some degree of redistribution. Here, more intensive supranational regulatory action occurs, often at the expense of national political and redistributive competences. This form of solidarity is typically reciprocity-based, ensuring that regulatory measures redistribute both advantages and disadvantages across Member States.

However, a third manifestation of solidarity appears to be slowly emerging, one that reflects a highly sophisticated level of EU action. This form suggests that the Union in certain areas has “matured” to the point of moving toward, or at least approximating, the concept of a “transfer union” as articulated by Nobel laureate Joseph Stiglitz.¹⁾ In essence, it would embody an expanded version of the Roman Civil Law concept of “obligatio in solidum”, now expressed in an EU-constitutionalised form, requiring Member States to assume shared responsibility in principle. Stiglitz defines a transfer union as a system in which Member States transfer resources to one another, even temporarily, in times of need. In principle, such a manifestation would imply an obligation for all Member States to contribute whenever necessary. Solidarity could thereby become solidarity among strangers, helping others in need, and hence not necessarily reciprocity-based. It would, in effect, be one for all; all for one.

These three simplified categories provide a broad, generalised framework. The first category is the least demanding, primarily anchored in cooperation and harmonisation, without significant resource transfers. The second category represents an intermediate level of commitment, centered on redistribution and typically reciprocity-based. Finally, the third category is the most committing, involving resource transfers – in a wide sense – that are not necessarily reciprocity-based. More specifically, the first category reflects the most common type of EU action, while the second signals a higher degree of intensity and obligation. The third category, by contrast, encompasses EU action at a more advanced level of solidarity.

Article 42(7) TEU

As a final consideration, it is worth noting the mutual assistance clause in Article 42(7) TEU. This provision stipulates that if a Member State becomes the victim of armed aggression on its territory, the other Member States are obliged to provide aid and assistance by all means in their power, in accordance with Article 51 of the United Nations Charter. Introduced by the Lisbon Treaty in 2009, the clause has historical roots predating its formal inclusion. To date, it has been invoked only once, by France following the 2015 Paris attacks. Article 222 TFEU serves as a complementary provision, though it differs in several important respects.

The provision serves two core functions. First, it formalises the mutual commitment of Member States to assist one another in the face of common threats. Second, it sends a clear deterrent signal to potential aggressors that any hostile act will trigger a unified response. In essence, Article 42(7) TEU thus operates both as a promise and as a warning.

By referring to “Member States” rather than EU institutions, Article 42(7) TEU establishes a mechanism for direct intergovernmental dialogue and support, bypassing the involvement of EU bodies. This structure enables an EU Member State to request assistance from other Member States even in scenarios where a given threat originates from a NATO ally, including the United States.

Greenland is likely to fall within the understanding of the “territory” of the EU Member State of Denmark, and thereby to be considered within the scope of Article 42(7) TEU. Given the nature of the provision, it would then be the responsibility of the Danish government, in coordination with the Greenlandic government, to invoke the clause and ensure that assistance is provided to the relevant parts of the Kingdom in the event of armed aggression.

Concluding reflections

“[S]olidarity […] is something that cannot be enforced – either it’s there, or it isn’t. I remember when during a debate on relocation at a European Council summit, it was suggested that, in our conclusions, we include the term ‘the obligation of solidarity’. I protested, saying this was an obvious oxymoron”.

With these words, Donald Tusk, then President of the European Council, captured in 2019 the enduring complexity and controversy surrounding both the substance and legal status of European solidarity. Considering today’s threat, the questions remain whether solidarity truly is present, and if so, whether Europe is prepared to express it not merely through the first, least demanding form of solidarity, but to advance toward the third, namely solidarity at its most profound and binding level.

As Article 42(7) TEU as explained serves two core functions, its deterrent effect on potential aggressors depends entirely on the credibility of mutual commitment among Member States. The warning is only effective if others are convinced that the promise of assistance is genuine and will be honoured. In short, the promise must be convincing for the warning to carry weight.

This consideration is critical in light of the current threat, where defending Greenland’s territorial integrity might appear increasingly urgent. Beyond geopolitical strategy, Europe must ask whether it is prepared to step up for its Greenlandic Union citizens and uphold its own objectives and values in an unprecedented way, and whether Member States, as an expression of solidarity, are willing to go so far as to engage in potential military action, sharing burdens and responsibilities collectively. Such a step would mark the emergence of a new, underdeveloped sub-category of solidarity: “defense solidarity.” In that scenario, Europe would adopt a firmer stance than ever before, transforming “words” into tangible force.

It may face a pressing need to communicate clearly to the world that Greenland is part of Europe. Moreover, it could swiftly consider whether and how Greenland – as well as Iceland and Norway, given their strategic presence in the Arctic – could be offered genuinely attractive and closer ties with the EU. It is worth recalling that, in addition to the Kingdom of Denmark, the Member States Sweden and Finland are also considered as Arctic states and have strong interests in these developments.

As Advocate General Sharpston once observed: “Solidarity is the lifeblood of the European project.” Today, an intensified form of European solidarity may well be the best path forward.