Through an ICJ Lense, Legal Attacks on Denmark’s Title to Greenland Would Fail

“You know, because a boat landed there 500 years ago and then left, that doesn’t give you title.” So said the American President upon departing for Davos. It should come as no surprise that Donald Trump challenges Denmark’s title to Greenland. A favorite tactic of real estate magnates is to strip the owner’s title to property they want to acquire. America’s interest in Greenland is not new; historically, its strategic importance has caused American governments to intermittently talk about acquiring it, most famously in 1946 when President Truman offered to purchase it for $100 million in gold, and later during the Eisenhower administration in a 1955 Joint Chiefs memo that was handily rebutted by a 1956 State Department memo.

However, President Trump’s renewed attention on this question has gone further. It is bolstered by bellicose comments from within his administration together with legislation being crafted in Congress to lay the legal groundwork for Greenland’s admission to the United States. American bluster and saber-rattling directed at its NATO ally Denmark has Europe and the alliance on edge. Trump has questioned Denmark’s claim to Greenland, and a legal notion to try to divest Denmark of title to Greenland, thereby opening it up to more forthright acquisition without damaging NATO, would rely on two theories: that Denmark’s sovereignty over Greenland rests on the discredited “doctrine of discovery” and, moreover, its claim to Greenland is in doubt in the wake of Britain’s loss at the International Court of Justice (ICJ) in the Chagos Archipelago case.

These arguments are legally unsound. More importantly, it misunderstands how modern international law evaluates territorial sovereignty—and risks destabilizing precisely the rules-based order the United States and its allies depend upon in the Arctic. The law moves forward, not backwards, and the law as it stands in 2026 requires that Greenlanders decide the future of Greenland – a position that is wholly in accord with governing Danish law. The jurisprudence of the ICJ points the way on why such arguments against Danish title would fail:

Discovery Is Not the Legal Test

It is true, the doctrine of discovery has long since ceased to function as an independent basis for territorial title. Even at the height of European colonial expansion, discovery alone was insufficient to establish sovereignty. In contemporary international law, it is legally irrelevant unless followed by something far more demanding: effective, peaceful, and continuous display of state authority.

That principle was classically articulated in the Island of Palmas arbitration (1928), a decision that remains foundational for the ICJ’s territorial jurisprudence. The arbitrator, Judge Max Huber, rejected discovery as a source of title in favor of effectiveness, holding that sovereignty depends on “the continuous and peaceful display of State authority.” The decision’s importance lies not in its age but in its durability: the ICJ has consistently embraced its logic.

The Court reaffirmed this approach in cases such as Burkina Faso v. Mali (1986), where it emphasized that stability, effectiveness, and the avoidance of legal vacuum are core values of territorial law. Borders are not historical abstractions to be endlessly re-litigated; they are legal facts, consolidated through governance and recognition. Denmark’s sovereignty over Greenland rests squarely within this framework. It is grounded not in symbolic acts of discovery but in centuries of administration, international acceptance, and judicial confirmation.

Greenland Is Not an Open Legal Question

Unlike many territories that become subjects of international dispute, Greenland’s status has already been adjudicated. In 1933, the Permanent Court of International Justice—the ICJ’s direct predecessor—decided the Legal Status of Eastern Greenland case between Denmark and Norway. Norway argued that Denmark lacked sovereignty over parts of Greenland and that those areas were effectively terra nullius. The Court rejected that claim in unequivocal terms, holding that Denmark possessed sovereignty over the whole of Greenland.

The decision rested on two interlocking grounds: Denmark’s long-standing exercise of authority and Norway’s own binding assurances recognizing Danish sovereignty, famously memorialized in the Ihlen Declaration. In modern ICJ parlance, this was a case of recognition, acquiescence, and estoppel operating together to consolidate title.

That judgment has never been overturned, questioned, or undermined by subsequent international practice. To the contrary, the international community has treated Greenland as Danish territory for nearly a century. In ICJ doctrine, this matters enormously. Territorial sovereignty, once judicially affirmed and followed by consistent state practice, becomes legally entrenched. Courts are loath to disturb such settlements absent extraordinary circumstances. Any argument that Denmark’s title is “invalid” because of discovery would therefore collide not only with modern doctrine, but with binding judicial history.

Decolonization Law Does Not Undo Denmark’s Sovereignty

Recognizing the weakness of a discovery-based argument, Trump’s proponents of a challenge to Denmark’s title to Greenland would be tempted to pivot to decolonization law, invoking the ICJ’s 2019 advisory opinion on the Chagos Archipelago. In that opinion, the Court held that the United Kingdom’s separation of the Chagos Archipelago from Mauritius during the decolonization process was unlawful and that the U.K. had an obligation to bring its administration of the islands to an end.

At first glance, Chagos might seem to offer a pathway for revisiting historical territorial arrangements. But on closer inspection, it does the opposite. The Court’s reasoning in Chagos was tightly tethered to a specific legal context: incomplete decolonization. Mauritius was a non-self-governing territory, and the detachment of Chagos in 1965 occurred under conditions that did not allow the Mauritian people freely to express their will. The Court treated self-determination as the controlling norm and held that colonial powers may not fragment territories in ways that frustrate that right.

Greenland today bears no resemblance to that legal posture. It is not a non-self-governing territory in the classic decolonization sense. It enjoys extensive self-government, its own parliament, control over internal affairs, and—critically—a legally recognized right to independence should its population choose it. Denmark has not only accepted that right but has embedded it in domestic law and affirmed it internationally.

This places Greenland squarely within the ICJ’s self-determination jurisprudence, not in tension with it. As the Court emphasized in Western Sahara (1975), self-determination requires the “free and genuine expression of the will of the peoples concerned.” Greenland’s constitutional arrangement is designed precisely to allow that expression over time. Chagos therefore does not stand for the proposition that colonial-era sovereignty is presumptively invalid. It stands for a narrower, more disciplined rule: colonial powers may not complete decolonization in a manner that denies self-determination. Applied correctly, that doctrine reinforces Denmark’s position rather than undermining it.

Stability Is a Central Value of Territorial Law

A recurring theme in ICJ territorial jurisprudence is the law’s preference for stability over historical revisionism. In the Temple of Preah Vihear case (1962), the Court emphasized reliance and acquiescence, holding that long-accepted boundaries should not be unsettled by belated objections. In Cameroon v. Nigeria (2002), it again stressed that stability and predictability are essential to peaceful international relations. This concern is not abstract. Borders structure expectations, security arrangements, and economic planning. Reopening settled sovereignty questions invites uncertainty—and, in contested regions, conflict.

The Arctic magnifies these stakes. As climate change accelerates access to Arctic routes and resources, legal clarity becomes a strategic asset. Undermining Denmark’s sovereignty over Greenland would not merely raise academic questions; it would inject uncertainty into NATO’s northern flank and invite opportunistic behavior by actors far less committed to the rule of law. From a U.S. perspective, this is not a theoretical concern. The United States benefits enormously from a legal order that treats sovereignty as stable once lawfully established. That same order underwrites U.S. positions from the South China Sea to Eastern Europe. Weakening it in the Arctic would be strategically self-defeating.

The Irony of a Discovery-Based Challenge

There is an additional irony in any U.S. argument premised on denouncing the doctrine of discovery and seeking to apply the law of decolonization. The ICJ is acutely sensitive to consistency and symmetry. Legal principles invoked to invalidate others’ sovereignty inevitably cast shadows closer to home. More fundamentally, international law has moved beyond discovery not by declaring all historically acquired titles illegitimate, but by changing the criteria by which sovereignty is assessed today. The law looks forward, not backward. It asks whether authority is exercised lawfully, whether populations enjoy self-determination, and whether arrangements promote stability and peace. Denmark’s relationship with Greenland answers those questions in the affirmative.

If Greenland’s status changes in the future, it will not be because an external power successfully reframed a settled legal order as a discovery-era or decolonization-era legal mistake. It will be because Greenlanders themselves choose a different political destiny. That is not a loophole in international law; it is its central moral and legal commitment. Greenland is not terra nullius. Denmark’s sovereignty does not rest on discovery or decolonization arguments. And at The Hague, as well as within the entire framework of public international law upon which much of American success in global affairs rests, those facts would matter—not only for Denmark, but for the integrity of the international legal system the United States has long championed.