Trump's Claim on Greenland: Legal Limits and Geopolitical Impacts

First, it is worth noting that the idea of acquiring Greenland faces several legal barriers. From a US constitutional standpoint, the purchase of foreign territory would require the negotiation and ratification of an international treaty by the Senate (two-thirds of the votes) and the approval of funds by Congress. In this case, Trump would need to ratify a treaty with Denmark and Greenland in order to purchase the world's largest island. In practice, he has neither a price nor a prior purchase agreement, especially regarding voluntary cooperation from Denmark or Greenland, nor sufficient support in Congress. In addition, US lawmakers have even proposed measures to legally prevent any transfer of sovereignty that would jeopardize US commitments, including Atlantic Alliance treaties.

At the international level, any attempt at annexation would violate basic principles of international law. According to scholars, the acquisition of territory through the threat or use of force is prohibited by the United Nations Charter and by the consensus of the post-World War II international system. The only peaceful form of territorial transfer would be consensual cession by treaty, as in the historical cases of the Louisiana Purchase (1803) or Alaska (1867), which would require acceptance by both parties. However, Greenland has a high degree of internal autonomy, in addition to being officially part of the Kingdom of Denmark: Copenhagen retains jurisdiction over foreign relations and defense. In 1933, the Permanent Court of International Justice confirmed that the island was Danish territory. Consistently, Danish and European authorities have repeated that “Greenland belongs to its people” and that it is not up to third parties to negotiate its sovereignty. Danish Prime Minister Mette Frederiksen went so far as to say that any American military attack against a NATO nation would mean the end of the alliance, emphasizing the unacceptable nature of unilateral actions.

For all these reasons, analysts consider Trump's claim to be without legal basis. Without an approved treaty and with outright opposition from Copenhagen and the Greenlanders themselves (who overwhelmingly reject annexation), there is no legal or political basis for the US to simply incorporate the island. As expert Michael Schmitt, quoted by Just Security, points out, Denmark's sovereignty over Greenland is indisputable under international law, so any attempt at conquest would flagrantly violate the territorial integrity of another country. In short, neither the US Constitution nor international law unilaterally authorizes the purchase or annexation of Greenland. Any such transaction would require a mutual agreement that is impractical under the current circumstances.

The prime ministers of Denmark and Greenland, Mette Frederiksen and Jens-Frederik Nielsen, said in a joint statement that Trump's pressure on the Greenlandic island was “unacceptable.” The Danish representative believes that, although the US president has toned down his rhetoric about acquiring the territory, he still wants to own Greenland. Nevertheless, the diplomatic crisis between Washington and Copenhagen has been intensified by the possibility of the Danish kingdom facing legal disputes due to the approval of an agreement that grants broad powers to the United States within its territory. Signed in 2023 and approved by the Danish legislature in 2025, the agreement gives the United States “unrestricted access” to air bases and grants it jurisdictional powers over civilians.

The claim that the pact is unconstitutional came from Deputy Theresa Scavenius, who plans to sue the Danish state on the grounds that the transfer of the country's sovereignty to another international authority requires the support of ⅚ of parliament for a constitutional amendment, as provided for in the 1953 Constitution, which does not apply to the defense agreement. Although it does not extend to Greenland, it appears that the bill could legitimize the use of force against Danish citizens by the United States, in addition to allowing US soldiers to curb protests in front of their bases, so as not to be covered by the Danish legal system.

Among the means available to Trump to achieve his goal of annexing Greenland to the United States are providing aid to the Greenlandic population, proposing to purchase the island, military intervention in the region, and, finally, ratifying an agreement to share sovereignty over the Arctic territory. In the first case, paying compensation to Greenland's nearly 56,000 inhabitants is an option being discussed by the US government, with a view to persuading the island's residents to break ties with the Danish kingdom and join the United States. Greenland's right to separate from Denmark has been provided for in the Self-Government Act since its revision in 2009. In addition, Washington's efforts to compensate Greenland's inhabitants could reach US$5.6 billion if the government paid US$100,000 to each citizen.

From Trump's perspective, the offer to purchase Danish territory in the Arctic is a more desirable alternative than the possibility of invading it. Any negotiations for the acquisition of Greenland by the United States would be subject to the consent of the Greenlandic and Danish authorities, who repeatedly affirm that the island is not for sale. Proposals for the acquisition of Greenland by the United States are not new to the Trump administration, with attempts dating back to 1867, when the first offer was made. Although the NATO Treaty condemns military attacks against any member state, the White House does not rule out the use of force to take over Greenland, which could constitute a violation of the principle of national sovereignty. The eventual ratification of a legal instrument establishing a unique model of shared sovereignty, such as the Compact of Free Association, would depend on Greenland becoming independent from Denmark and would establish US control over defense and security issues, in addition to economic assistance.

Trump's pressure on Greenland has caused significant internal tensions within NATO. Allied governments reacted unanimously to the threat against a member territory: Denmark stated that the defense of Greenland is a concern shared by NATO and organized a ministerial meeting with Washington to discuss security in the Arctic. Seven European leaders issued a statement reinforcing that Greenland belongs to its people and that only Denmark and Greenlandic authorities can decide on its future, noting that all NATO allies are obliged to comply with the principles of the UN Charter, including issues concerning sovereignty, territorial integrity, and the inviolability of borders. This reaction in defense of an ally's integrity took place in a climate in which Prime Minister Frederiksen herself warned: “If the US decides to attack another NATO country militarily, then everything would stop—including NATO,” summarizing the fear of a split in the bloc if a member breaks its alliance.

Furthermore, the coercive measures suggested by Trump (such as imposing tariffs on opposing European allies) have shaken mutual trust between the states. An analysis of this situation highlights that American threats have sparked debates about the European Union's use of trade defense instruments, shifting the transatlantic relationship from strategic cooperation to economic deterrence among allies. In other words, by using trade pressure and bellicose rhetoric, the US president has undermined NATO's central principle: the conviction that external threats would be faced collectively, not exploited for internal bargaining. This dynamic has partly undermined the “central principle of NATO”—the confidence that allies would not attack each other or manipulate mutual guarantees for momentary interests.

In response to the crisis, European allies sought to demonstrate unity. In Greenland, Denmark, the United Kingdom, Norway, Sweden, France, and Germany sent symbolic contingents to train together and signaled that no attempt at annexation would be accepted by the “Old Continent.” Danish Foreign Minister Rasmussen himself commented that, although the US “shares some concerns,” there is no reason to annex the territory—the focus is on finding common ground in defending the Arctic. Internally, NATO Secretary General Mark Rutte spoke directly with Trump to avoid escalation and stressed that debates are part of a “coalition of democracies,” but that the alliance must always focus on its common goal of collective defense. Belgian Minister Theo Francken even compared the organization to a “76-year transatlantic marriage,” in which there are sometimes crises, but in which general alignment around mutual defense prevails.

Many observers see the controversy as an unprecedented stress test for NATO. Rutte herself and other allies emphasized that, despite the differences, the Alliance managed to refocus on its constitutional mission (Article 5). However, analysts have warned that the mere possibility of one ally questioning another's territory constitutes a “dangerous precedent,” as it conveys the perception that mutual protection commitments can be relativized by immediate national interests. For many, the episode highlighted deep cracks in NATO's political cohesion at a critical moment—especially with the war in Ukraine ongoing. As can be seen, each “internal crack in the West” silently favors revisionist powers such as Russia. In fact, fears have been raised that disagreements arising from this dispute could weaken Western support for Ukraine and the very credibility of the alliance's deterrence in the Baltic and Arctic regions. Although the war in Ukraine still mobilizes the commitment of most allies, many experts believe that, in the short term, the Greenland crisis has strained transatlantic ties and accelerated debates on responsibility sharing and strategic priorities within NATO.

In Davos, President Donald Trump declared that he did not plan to take Greenland by military force, emphasizing the use of mechanisms such as imposing tariffs and negotiations to discuss the acquisition of the island. For him, the incorporation of Denmark's autonomous territory would be fundamental to preserving the national security interests of the United States. In his speech, Trump asked the Danish kingdom to make a decision and requested the opening of negotiations on the conditions necessary to take control of the island.

Furthermore, the US president distorted historical facts relating to the post-World War II period by stating that the United States held the island under Washington's administration and “respectfully” returned it to Denmark. However, since the early 18th century, Greenland has been under Danish rule, following a gradual process of consolidating greater political and legal independence from Denmark. Currently, Greenland is an autonomous territory whose internal politics are conducted by local authorities, while foreign policy, defense, and security are administered by Copenhagen.

In characterizing the United States as “a child of Europe” in his speech at the Munich Security Conference, US Secretary of State Marco Rubio presented a new partnership proposal, stating that both continents belong to each other. According to him, the United States under Trump was not seeking a weak or guilt-ridden Europe, but a renewed alliance that recognizes that current problems stem not only from bad policies, but also from a widespread sense of hopelessness and complacency. In his speech, Rubio told Europe that the United States wants a renewed alliance, but on Trump's terms, urging the continent to support them in building a new world order. At the event, Rubio met for 15 minutes with the Prime Minister of Denmark and the Prime Minister of Greenland, on which occasion they agreed to continue negotiations on the administration of Greenland. According to Nielsen, representative of the autonomous territory, it was emphasized that the ongoing negotiations represent the appropriate path, with Greenland's interests having been repeatedly and clearly highlighted. The Danish prime minister announced that activities will continue as agreed within the high-level working group. Trump claimed that the United States is currently negotiating ownership of the island.