The prospect of a United States attempt to seize Greenland has raised an unprecedented question for Nato, whose founding treaty does not clearly address the possibility of one member attacking another. Article 5, the cornerstone of mutual defence, states that an armed attack on one ally in Europe or North America shall be considered an attack on all. Yet its application becomes ambiguous when the aggressor is the alliance's most powerful member.
Denmark's prime minister, Mette Frederiksen, said on Monday that if the US chose to attack another Nato country, 'everything will stop'. The remark followed months of transatlantic tension, including Donald Trump's campaign statement that he would not protect 'delinquent' members failing to meet defence spending targets, and his defence secretary Pete Hegseth's assertion in February that the US was no longer 'primarily focused' on defending Europe.
Diplomacy before June's Nato summit appeared to ease the discord, with allies agreeing to raise defence spending to 3.5% of GDP by 2035. However, Marion Messmer, a director at Chatham House, questioned whether the strategy of flattering Trump was sustainable. 'Yes, the summit went well in that Rutte found formulations that flattered Trump. But I'm not sure how far that is a sustainable strategy,' she said.
The territorial appetite for Greenland resurfaced after the capture of Venezuela's Nicolás Maduro, with the US explicitly challenging Denmark's historical sovereignty. Trump's adviser Stephen Miller insisted that the real world was 'governed by strength, that is governed by force, that is governed by power', rather than treaties. The imbalance in military capability is stark: the US has 1.3 million active personnel compared with Denmark's 13,100, and its 2025 defence budget of $845bn exceeds the combined $559bn of the other 31 allies.
Nato's founding treaty contains no provision for expelling a member, even if one were to turn on another. Nevertheless, analysts argue that such a move, even over an Arctic territory with fewer than 60,000 inhabitants, would undermine the credibility of the 76-year-old alliance at a time of heightened Russian aggression, leaving the organisation intact but fundamentally questioned.
