As the New York Times reported, President Trump and NATO have reached the framework of a deal that would grant the US sovereign bases over territories of Greenland. One of the officials present at the negotiations compared the proposed bases to the British Sovereign Base Areas (SBAs) in Cyprus, a comparison that has also been analysed by Marc Weller in a recent blog post. We argue that establishing such bases constitutes a violation of international law and cannot validly be agreed to by Denmark or NATO. This conclusion draws support from two distinct lines of argument: one relating to the (il)legality of establishing sovereign bases; and the other to indigenous rights.

Who May Consent to Sovereign Bases?

The first line of argument draws on the ICJ’s Chagos Archipelago Advisory Opinion. In this, the Court explained that the detachment of part of a non-self-governing territory must be based on the free and genuine will of the people of the concerned territory. If one is concerned about respecting “the free and genuine will of the people”, identifying said people is crucial. Denmark’s title to Greenland is uncontested in modern practice and has been expressly recognised by the United States in the 1951 Defense of Greenland Agreement and its 2004 update. While Denmark’s claim to Greenland has been described as “unimpeachable,” Greenlanders are constitutionally recognised as a “people” with a right to self‑determination, including a lawful pathway to independence by referendum and subsequent negotiation. If anyone were to consent to the creation of US sovereign bases, therefore, it would have to be them. It is not for Denmark to reach such an agreement, and it is certainly not for the NATO Secretary General.

Denmark’s sovereignty over Greenland was abruptly questioned when President Trump declared that the US had to own the island and did not rule out using force to achieve this. In light of such threats, it is clear that if a transfer of sovereignty were to take place, it would not be the result of “the free and genuine will of the people”. Also supporting this argument is the fact that a threat of the use of force by the US violates Article 2(4) of the UN Charter, which is a ius cogens norm. Thus, any transfer of sovereignty of part of Greenland’s territory to the US, as a result of such a threat, would be null and void.

Modelling the proposed US bases on the SBAs in Cyprus does not enhance their credibility. The SBAs are a remnant of Cyprus’ colonial history, but even when seen through this light, they are arguably illegal. The Treaty of Establishment 1960 that created the SBAs allowed the UK to retain its sovereignty over the two large bases, while at the same time, granted independence to the rest of the island. Yet, the UK’s sovereignty is not unlimited: Appendix O of the Treaty (which Cyprus considers to be legally binding, but the UK does not) declares the UK’s intention “[n]ot to set up or permit the establishment of civilian commercial or industrial enterprises”; prohibits the creation of “custom posts or other frontier barriers” between the SBAs and the rest of the island; and mandates that UK law in the SBAs will “mirror” that of the Republic of Cyprus. As one of us has already argued (here and here), even with such restrictions on the UK’s sovereignty, the SBAs remain of doubtful international legality, precisely because they were established in contravention of the principles set out in Chagos.

The establishment of SBAs might have been considered acceptable in the era of decolonisation, but not anymore. Contemporary practice to establish military bases overwhelmingly no longer grants this type of enclave sovereignty within the host state, but only grants defined functional (exclusively military) rights to the sending state. Problematically, what President Trump envisions in Greenland are not just SBAs, but “SBAs plus”, which would allow the US to not merely use the bases for military purposes, but also develop them commercially. Thus, any future Greenland “framework” built on sovereignty transfers would in our view not just “trade short‑term optics for long‑term legal uncertainty”. Instead, it would constitute an overt violation of international law.

Indigenous Rights, Environmental Due Diligence, and Climate Obligations

The second line of argument for why US sovereign bases in Greenland would be illegal relates to the protection of indigenous rights. Where indigenous lands, territories or resources are affected, the UN Declaration on the Rights of Indigenous People, as customary international law, requires processes oriented toward Free, Prior and Informed Consent for large‑scale, high‑impact measures. Such consent must be supported by prior environmental and social impact assessments and equitable benefit‑sharing. A sovereignty carve‑out for enclaves would plainly qualify; without demonstrably robust consent from Greenlandic/Inuit institutions, it would conflict with today’s Indigenous‑rights baseline. The International Law Association’s 2020 Guidelines likewise affirm duties of rational, sustainable and safe resource management with particular regard for indigenous rights, and embed transparency, public participation, access to information and justice, and benefit‑sharing.

The ICJ’s 2025 Climate Advisory Opinion closes remaining gaps by integrating fields that once were siloed. The Court confirmed that environmental treaties, the customary no‑harm rule and duty to cooperate, and international human rights obligations operate cumulatively. It articulated a stringent due‑diligence standard, required impact assessments for activities posing significant environmental risks, recognised the right to a clean, healthy and sustainable environment, and characterised key obligations as erga omnes (for an accessible synthesis of the Advisory Opinion, see here). Applied to Greenland, a sovereignty enclave that removes areas from Danish/Greenlandic jurisdiction would impede the host’s ability to carry out due‑diligence controls, run cumulative EIA/ESIA processes with public participation, and secure the clarified human‑rights baseline – problems that do not arise when access is organised under host‑state sovereignty through normal international treaties for stationing of foreign militaries and their bases. This is exacerbated by US law, which does not treat sovereign bases such as Guantanamo as US territory, i.e. neither US domestic nor international law would fully apply.

Rather than starting a resource “race to the Arctic”, States should embrace the spirit of the Arctic Council.¹⁾ While most Arctic Council outputs are non-binding recommendations, Member States could potentially conclude a new binding instrument associated with the Council focused on de-militarization. Such an agreement could limit military use of the Arctic Ocean in the spirit of the BBNJ agreement, similar to how the Antarctic Treaty operates. Indigenous representatives on the Arctic Council participate fully in its drafting.²⁾ It feels deeply disturbing that one of the countries that has withdrawn from the constitution of climate change in the form of the Paris Agreement would use the warming of the Arctic Ocean as an excuse to lay sovereignty claims on Greenland.

In twenty-first-century international law, carving out a sovereign enclave, “forever” as President Trump called it, constitutes multiple breaches of international law. Any move towards US sovereign enclaves in Greenland would contravene the UN Charter and ius cogens norms, the right of self-determination, and the rights of indigenous peoples; it would undermine Denmark’s and Greenland’s ability to discharge binding environmental and human‑rights duties, and it would depart from prevailing practice for military bases. It should be ruled out.

The post Why US Sovereign Bases in Greenland Would Violate International Law appeared first on Verfassungsblog.