Federica Fazio

Ever since Donald Trump announced his bid for the 2024 presidential election, NATO allies have been looking for ways to “Trump-proof” the alliance. During his first term, Trump had in fact frequently complained that NATO was too much of a burden on the United States, even threatening to withdraw from the alliance at the 2018 Brussels Summit if members didn’t meet the two per cent GDP defence spending target agreed in Wales in 2014.

Following Trump’s re-election in November, European allies have grown increasingly worried that the President-elect might not honour the mutual defence pledge if one of them were attacked by Russia, whose war of aggression against Ukraine is now approaching its fourth year.

When interviewed by NBC News roughly a month after his victory and asked if the US would stay in NATO under his upcoming presidency, Trump responded: ‘They have to pay their bills. If they pay their bills, absolutely.’ But he made it clear that if they didn’t, he would seriously think about getting out.

A few days before Christmas, the Financial Times then reported that Trump’s team had told European leaders that he plans to demand they raise defence spending to five per cent, though he might settle for 3.5 per cent.

What no one could have imagined is that, weeks from his inauguration ceremony, Trump would start to threaten two fellow NATO allies, Canada and Denmark, the latter also being an EU member.

In December, he proposed implementing a 25 per cent tariff on Canadian goods, repeatedly suggesting that Canada should become the US’ 51st state. As for Denmark, he expressed a renewed interest in acquiring Greenland from Denmark, something he had first showed an interest in during his first term in office, citing national security considerations.

In recent weeks, Trump has stepped up his rhetoric about the idea of annexing Canada and Greenland. During a news conference at Mar-a-Lago on 7 January, he floated the possibility of bringing these territories into the US. Later that day, he took to Truth Social to post two maps of North America, showing the US and Canada merged into a single country. He also shared a satirical imitation of a New York Post front cover, featuring Trump himself pointing at a map with Canada and Greenland marked with red ‘X’s and relabeled ’51st’ and ‘Our Land’, respectively.

Hence the question: what happens if Trump invades Greenland? 

A 1951 agreement, amended in 2004, exists between the US and Denmark concerning the defence of Greenland and remains valid to this day. While this agreement underscores the collaborative defence relationship between the two NATO nations, it is as an executive agreement, which Trump could potentially pull out from with a stroke of his pen. Unlike treaties, executive agreements don’t need Senate approval, so the President can easily withdraw from them without the Senate having a say.

Congressional involvement in treaty termination, on the other hand, is much more controversial. This is because the US Constitution clearly outlines the process for negotiating treaties, which requires a two-thirds Senate majority, but it doesn’t address how to terminate them. For example, while Trump single-handedly withdrew the US from the Paris Agreement during his first term, it is written into US legislation that leaving NATO would require the advice and consent of the Senate or an act of Congress. This lack of clarity has fuelled ongoing debates over whether Congress should play a role in the process.

In the event of war, in line with Art. I § 8 of the US Constitution, under the 1973 War Powers Act, the President is required to notify Congress within 48 hours of committing armed forces to military action. Additionally, without a declaration of war or specific statutory authorisation, the military can’t stay involved in hostilities for more than 60 days, plus a 30-day withdrawal period.

So, if Congress doesn’t either provide authorisation for the use of military force (AUMF) or declare war against Greenland, both highly unlikely scenarios, Trump would need to end military operations within that timeframe. The resolution, however, has been violated several times in the past, and 60 days could be more than enough time to seize control of Greenland.

Situated east of the Canadian Arctic Archipelago, Greenland is the world’s largest island and has been a part of Denmark since 1721.

However, the country was granted home rule in 1979 and, since 2009, has functioned under a Self-Government Arrangement, providing it with the authority to negotiate and conclude agreements under international law with foreign states and international organisations, except in matters of foreign, defence, and monetary policy.

Calls for independence have been progressively growing under Prime Minister Múte Egede, especially following Trump’s renewed interest in Greenland. Under the aforementioned 1951 agreement on the defence of Greenland, the island is home to the US military’s Pituffik Space Base, which hosts Upgraded Early Warning Radar (UEWR) systems for early detection and precise tracking of ballistic missiles.

While Greenland is covered by Article 5 of the 1949 North Atlantic Treaty (NAT), it might not be covered by Article 42.7, the EU’s mutual assistance clause which was brought into the Treaty on European Union (TEU) in 2009. Here is why:

Article 5 NAT stipulates that for collective defence to be invoked within NATO, an armed attack against one or more NATO allies must occur in “Europe or North America”. Article 6 further specifies that this includes attacks perpetrated “on the territory of any of the Parties in Europe or North America… or on the Islands under the jurisdiction of any of the Parties in the North Atlantic area north of the Tropic of Cancer”.

Although Greenland is not specifically singled out in the Alliance’s third Strategic Concept of 1957 (MC 14/2), which clarified the geographical scope of NATO’s Art. 5, the document states that “(a)ll the islands in the North Atlantic and the Norwegian and Greenland Sea areas of the Arctic Ocean belong to NATO nations”. Additionally, the NATO Status of Forces Agreement has applied in Greenland since 1955.

Article 5 NAT, however, can’t be invoked by one NATO ally against another, as it would contradict the very spirit of the Alliance. Even if a NATO ally invoked the clause against another, all 32 member states would need to unanimously agree in the North Atlantic Council that the actions in question amount to an armed attack. Without consensus, no measures can be taken under Art. 5, even if a single member objects. The US would certainly object.

Article 42.7 TEU, in contrast, would potentially allow an EU member state like Denmark to seek assistance from other EU members if it faced aggression from a NATO ally like the US. After all, Turkey, a NATO ally, and Greece, like Denmark a member of both NATO and the EU, have been on the brink of conflict several times, most recently in 2020, when Greece even hinted at activating Article 42.7 TEU.

For the EU mutual assistance clause to be triggered, a member state must be victim of armed aggression “on its territory”. Unlike Art. 5 NAT, there is no further clarification regarding geographical coverage. Therefore, at least in principle, overseas territories outside of Europe should be considered within the scope of Art 42.7 TEU.

However, there are two types of overseas territories: Outermost Regions (ORs) and Overseas Countries and Territories (OCTs).

ORs are fully-fledged EU regions and part of EU territory. As such, they are subject to EU law and all the rights and obligations that come with EU membership, although some specific measures apply.

OCTs, are, instead, territories associated with the EU and not part of it. EU law does not apply to these territories, although their foreign, security and defence policies often fall under the jurisdiction of the EU member states with which they maintain special ties. 

Since EU law applies to ORs but not OCTs, it has been argued that Art. 42.7 TEU could be invoked for ORs but not OCTs. While Greenland joined the European Community alongside Denmark in 1973, it withdrew in 1985 following a referendum. Since then, the island has been categorised as an OCT.

Therefore, at present, Denmark might not be able to invoke Art. 42.7 TEU if Greenland were attacked by the US, although France’s Foreign Minister, Jean-Noël Barrot, recently appeared to suggest otherwise. It is important to note that the status of ORs and OCTs is not fixed; it can be modified by the European Council, at the request of the concerned EU member state, without amending the Treaty on the Functioning of the European Union (TFEU). This process was exemplified by the change in status of Mayotte in 2014.

Even if Greenland were reclassified as an OR and Denmark subsequently invoked Article 42.7 TEU, or invoked Art. 42.7 regardless of Greenland’s classification, the move would be merely symbolic. European nations lack the military force required to effectively stand up to the US; the EU’s only effective weapon against a US offence would be its economic leverage, particularly in the form of trade restrictions, such as tariffs, or sanctions targeting specific sectors of the US economy.

Although no unanimous decision of the Council is required for Art. 42.7 TEU to be implemented, the fact that the process is member state-driven and assistance would be provided bilaterally would likely lead to fragmentation within the EU. While some countries, like France, might be willing to offer support, others, like Hungary or Italy, might not, and there is no sanctioning mechanism that could compel them to do otherwise. Additionally, those countries that are both in the EU and in NATO could be subject to competing requests for assistance from both Denmark and the US.

A decision by the incoming Trump administration to invade Greenland would, therefore, also have deep consequences for NATO. In the best-case scenario, it could cause similar divisions within the alliance and erode trust among its members, while in the worst-case scenario, it could trigger a major identity crisis, as the very country NATO has relied on for protection over the last 75 years would now be the one it would need protection from.

Federica Fazio is a PhD candidate in the School of Law and Government at Dublin City University. Her research interests lie at the intersection of international law and international relations, with a substantive focus on transatlantic security and defense and EU-NATO relations. This article first appeared on the DCU Brexit Institute blog.