Regardless of whether the US administration’s renewed threat to annex Greenland materializes, its multiple legal ramifications warrant serious analysis under public international law and within the EU legal order as mediated by Danish domestic law. President Trump has not only refused to rule out the use of military force to acquire Greenland but has also repeatedly doubled down on his annexation ambitions, transforming what might once have been dismissed as rhetorical provocation into a credible geopolitical scenario.

The legal complexity is unprecedented precisely because multiple frameworks intersect, and their exact interpretation remains undefined. International law prohibits the acquisition of territory through force or the threat of force (Article 2(4) UN Charter), yet the threshold at which economic pressure constitutes unlawful coercion remains contested. NATO allies are committed to the peaceful settlement of disputes (Article 1 of the North Atlantic Treaty), but the treaty provides no guidance on how to respond when one ally threatens another’s territorial integrity. EU law adds a further layer: Article 42(7) TEU mandates mutual aid and assistance (“by all the means in their power, in accordance with Article 51 of the United Nations Charter”), raising the unresolved question whether and how this obligation applies to Danish territory lying outside the EU’s territorial scope, and notably whether economic coercion, however severe, can constitute “armed aggression” within the meaning of the Charter’s self-defense framework.

Greenland itself complicates the picture further. While Denmark retains sovereignty, the 2009 Self-Government Act recognizes Greenlanders as a people under international law with a right to self-determination. This raises foundational questions about whose consent is legally required for territorial transfer, whether self-determination permits territorial transfer to a third state rather than only independence (or continued association with Denmark), and how such claims interact with the principle of territorial integrity and the prohibition on coerced consent.

Beyond doctrine lie questions of enforcement and response. Could Denmark invoke Article 42(7) TEU, and what would “aid and assistance by all the means in their power” require when the source of the threat is also a NATO ally and the foundation of European collective defense? What roles could the ICJ, the UN General Assembly, or non-recognition doctrines realistically play given the United States’ veto power in the Security Council and withdrawal from compulsory ICJ jurisdiction? To what extent could economic countermeasures be justified under the law of state responsibility as responses to internationally wrongful acts, and would they remain compatible with WTO obligations or qualify as justified exceptions? Domestic constitutional constraints, be it in Denmark or Greenland, add yet another layer of complexity.

This Verfassungsblog Spotlight brings together legal experts to address these intersecting questions across international law, EU constitutional law, NATO obligations, and Danish constitutional requirements. While existing commentary has examined isolated aspects of the Greenland question (and a burgeoning list of comments is emerging), comprehensive analysis of how these legal regimes interact – and of the concrete response options they provide – remains largely absent. The urgency lies not in predicting whether annexation will occur, but in clarifying the legal frameworks that would govern such a scenario, the obligations they impose, and the mechanisms they provide for prevention and response.

This introductory contribution focuses on Greenland’s legal status under international law and EU law in the light of Danish domestic law. Other substantive questions, such as whether international law prohibits the methods the United States threatens to employ, whether Article 42(7) TEU’s mutual defense clause applies, what enforcement mechanisms exist, will be addressed by subsequent contributions. This contribution establishes the necessary legal foundation.

Greenland’s Legal Status

Any assessment of the legal implications of potential US annexation must begin with (i) Greenland’s status under international law, (ii) EU law, and (iii) Danish constitutional law. This status determines which legal frameworks apply to such a scenario, whose consent territorial transfer would legally require, and what obligations it would trigger for third states.

International Law: Danish Sovereignty with Recognized Self-Determination

Greenland is not a sovereign state and possesses no independent international legal personality. It is geographically classified as part of North America but owing to its historical ties with Denmark, formalised through Danish colonial administration beginning in the early eighteenth century- it is generally perceived as European. As part of the Kingdom of Denmark (Rigsfællesskabet), a state comprising Denmark, the Faroe Islands (a third country in the EU context), and Greenland (an EU overseas country and territory), Denmark retains full sovereignty over Greenland under international law – as the Permanent Court of International Justice confirmed in 1933. This includes exclusive competence over foreign affairs, defense, security policy, and the conclusion of treaties with defense or foreign policy implications. Under international law, any territorial transfer requires the sovereign state’s consent.

However, the 2009 Act on Greenland Self-Government (replacing the 1979 Home Rule Act) recognizes in its preamble “that the people of Greenland is a people pursuant to international law with the right of self-determination”. This constitutes the first explicit recognition in Danish legislation of Greenlanders as a distinct people holding self-determination rights. The Act transfers substantial competences to Greenland’s parliament (Inatsisartut) and government, including natural resources, subsurface rights, and mineral extraction –  economically critical given Greenland’s rare earth deposits and hydrocarbon potential. Denmark retains competence over constitutional affairs, monetary policy, foreign affairs, defense, and serves as the final court of appeal through the Danish Supreme Court.

Section 21 of the Self-Government Act establishes a procedure for independence: “Decisions on Greenland’s independence shall be taken by the people of Greenland”. If the Greenlandic parliament initiates independence negotiations and a majority of Greenlanders approve in a referendum, Section 21 commits Denmark to respect this decision and negotiate independence terms. Critically, the Act contemplates only two outcomes: continued association with Denmark or independence, not the transfer to a third sovereign. Whether the recognized right to self-determination extends to voluntary subordination to a new sovereign power remains legally unresolved. The 1970 Declaration on Friendly Relations, widely regarded as an authoritative interpretation of fundamental UN Charter principles and reflecting customary international law, identifies modes for realizing self-determination as “the establishment of a sovereign and independent State, the free association or integration with an independent State or the emergence into any other political status freely determined by a people”. However, state practice and ICJ jurisprudence have predominantly interpreted these modalities in decolonization contexts, as pathways from dependent or colonial status to self-governance through independence, continued association with the former administering power, or integration with that power. While a few contested cases exist where territories have changed sovereign allegiance (such as Western New Guinea’s transfer to Indonesia in 1963 or Northern Mariana Islands’ integration with the United States in 1986), whether voluntary transfer to a major power with no prior constitutional or administrative connection constitutes a legitimate exercise of self-determination lacks clear precedent in international law and remains doctrinally contested.

This confirms that despite being “one of the essential principles of contemporary international law” – as established by the ICJ in East Timor (Portugal v Australia) -, the principle of self-determination also remains one of the most unsettled norms in international law especially when applied beyond the colonial context, and it has been described as ‘plagued by an excess of indeterminacy both in terms of scope and content’

EU Law: OCT Status and Territorial Scope Questions

Greenland’s relationship with the European Union is sui generis and is primarily mediated through Denmark. Having been first recognised as a former colony of Denmark, Greenland maintained formal relations with the EU since 1973, when, in the aftermath of Denmark’s accession to the European Communities (EC), Greenland was included as part of Danish territory. Yet, it is worth noting that during the 1972 Danish referendum on EC membership, Greenland was not afforded the chance to hold a separate referendum. Had it done so, the result would have been negative, as a clear majority of Greenlanders—approximately 70 per cent—voted against EC membership.

Following growing tensions over fisheries policy, essentially Greenland’s economic lifeline, a 1982 consultative and non-binding referendum resulted in 52% voting to leave the EEC. As a result, in 1985, Greenland became the first territory to ‘exit’ from the European Communities through a negotiated legal process and remained the only example until Brexit. Legally speaking, it was not a ‘withdrawal’ as Greenland was not a Member State of the EU but was, and remains, part of an EU Member State, Denmark. The exit from the EC took place in the form of a reduction of the territorial jurisdiction of the Treaties through a Treaty change ratified by all Member States. The referendum sought to determine whether the EC Treaties should continue to apply in Greenland, and not address the potential transition to an OCT status. Yet, due to its former status as a colony, its geographical distance from the EU and in line with Greenland’s wishes, both developments took place. Greenland became an ‘associated overseas territory’ (Article 204 TFEU) with special arrangements with the EU, particularly with regard to fisheries (it is given access to the single market for fisheries’ products in return for EU fishermen’s access to Greenland waters (Protocol 34 to the Treaties)). This status provides special association, including development cooperation, duty-free market access for Greenlandic products, and participation in certain EU programs, but excludes Greenland from EU primary law’s application, including the Common Foreign and Security Policy (CFSP) and Common Security and Defence Policy (CSDP). Greenlanders retain EU citizenship through their Danish nationality, but do not reside in EU territory for treaty purposes.

This OCT status raises a critical legal question revolving around the so called EU’s “mutual assistance clause” (also referred to as mutual defense clause): When Article 42(7) TEU (an attack on one is an attack on all) refers to armed aggression “on [a Member State’s] territory” does this encompass Danish sovereign territory that withdrew from the EU in 1985 and holds OCT status? The prevailing interpretation suggests Article 42(7) covers territories to which EU law applies but not OCTs listed in Annex II. This is the position held by Bob Deen, Dick Zandee, Adája Stoetman at Clingendael, Federica Fazio, Hermann-Josef Blanke and Stelio Mangiameli.  However, this narrow reading is contested as: “its territory” in international legal usage encompasses all sovereign territory of a Member State, and excluding OCTs would create a dangerous gap in collective defense, allowing adversaries to target Member States’ peripheral territories with impunity.  Proponents of this broader interpretation include Ulla Neergaard (here and here), and Dimitry Kochenov. The question remains unresolved in the absence of authoritative interpretation by the Court of Justice or definitive state practice, and will be further explored by other contributors to this Spotlight. It is worth recalling, finally, that the mutual assistance clause has been invoked only once since its introduction by the Lisbon Treaty in 2009, when France activated it following the terrorist attacks (at the Bataclan) in Paris in 2015. Moreover, the question about the possible consequences of one NATO ally invoking the EU mutual assistance clause against another is not new: it was first raised by the then Greek foreign minister in response to a potential confrontation with Turkey.

Danish Constitutional Law: Dual Consent and Procedural Requirements

Under Danish constitutional law, any territorial cession would require compliance with procedures for constitutional amendments and potentially referenda under the Danish Constitution (Grundloven), though the precise requirements remain subject to interpretation given Greenland’s unique self-government status. The Constitution does not explicitly address territorial cession, creating uncertainty as to whether such a fundamental change would require the procedure under Section 88 (constitutional amendment, requiring two successive parliamentary votes with an intervening election and a confirmatory referendum) or whether ordinary legislative action with a qualified majority might suffice.

What is clearer is the framework established by Greenland’s self-government arrangements. As anticipated, the Self-Government Act of 2009 (Selvstyreloven), which superseded the 1979 Home Rule Act, establishes in Section 21 that if Greenland’s people decide in favour of independence, negotiations shall commence between the Danish Government and Naalakkersuisut (the Greenlandic government) regarding the introduction of independence.

This creates a dual-consent architecture: Denmark retains sovereignty and must act through its constitutional procedures, while Greenland holds what amounts to a veto over fundamental changes to its political status through its self-government institutions.

Whether a transfer to a third state would require the same procedures as independence, or whether such a transfer is legally contemplated at all, remains ambiguous, as the Act explicitly addresses only independence or continued association. The legal architecture established in 1979 and refined in 2009 was designed for a binary choice: deeper integration with Denmark or eventual independence. Transfer to a third sovereign power simply does not appear in the constitutional framework, raising the question of whether such a transfer falls outside the legally permissible exercises of self-determination under Danish law.

The interaction between these domestic constitutional requirements and international law principles on coerced consent will be explored by subsequent contributions examining the validity of consent obtained under duress. The critical question is whether constitutional procedures, referenda, parliamentary votes, and negotiations between Danish and Greenlandic authorities can function meaningfully when subjected to overwhelming external economic or military pressure. Does extreme coercion render constitutional procedures mere formalities incapable of validating what international law prohibits? Or can constitutional law maintain its integrity and gatekeeping function even under duress?

Conclusions

This contribution strived to pin down several foundational points for the legal questions raised by America’s threat of annexation, regardless of its form, of Greenland. The contributions that follow build on such a framework to examine these substantive questions in depth. What emerges clearly from this foundational analysis is that Greenland’s unique status, simultaneously a Danish sovereign territory, a self-governing entity with recognized self-determination rights, an OCT outside the EU’s geographical scope, and an Arctic territory of immense strategic importance, creates legal ambiguities precisely where clarity is most needed. The question of how international law, EU law, and Danish constitutional law would respond to coercive or even consensual annexation attempts requires careful examination.