U.S. Space Force Col. Susan Meyers, 821st Space Base Group commander, left, greets Vice President JD Vance and Second Lady Usha Vance at Pituffik Space Base, Greenland, 28 March 2025. Vance was the first vice president to visit the remote base, where he received an in-depth brief of the missions and importance to national defense.  U.S. Space Force / Staff Sgt. Jaime Sanchez

At a World Economic Forum event in Davos in January, US President Donald Trump ruled out using force to acquire Greenland, a semi-autonomous island belonging to Denmark, America’s NATO ally. He also moved away from imposing tariffs on NATO allies who didn’t support his claim for the ‘big, beautiful piece of ice’. Earlier in the month he had threatened such tariffs while refusing to deny that he might use the military to obtain Greenland for the US.

For its part, the Trump administration asserts that Greenland is under threat from Russia and China and that the US wishes to control the island for national security reasons. President Trump has said that the US would be better placed to defend Greenland in the event of an attack than Denmark would.

At the same time, the realisation by NATO allies that the US is no longer a reliable ally will lead European counties to take more responsibility for the continent’s security. The result may be a strengthened alliance with a stronger role for Europe, says Federica D’Alessandra, Co-Chair of the IBA Rule of Law Forum. ‘That being said, the damage in terms of trust is as significant as it has ever been. After Trump, the political leadership in [the] US will have a lot of work to do to repair this damage,’ she adds.

A weakened NATO could have far-reaching consequences for Ukraine. While the country is under siege from Russia, predictability, coordination and strategic planning among NATO allies is crucial for sustaining the war effort. A diminished NATO would also have implications for other support provided to Ukraine – for example, in terms of weapons, intelligence, communications and training.

‘Ukraine is not passively observing these risks’, says Anna Babych, Chair of the ESG Group of the IBA European Regional Forum. The country is involved in strengthening instruments such as the European Peace Facility – a funding initiative to help the EU prevent conflicts – and the European Defence Fund, which supports companies across the bloc’s Member States in developing competitive and collaborative defence projects. Ukraine is expanding bilateral security arrangements – including the UK-Ukraine defence partnership – as well as diversifying procurement and expanding its domestic defence production.

However, without US involvement, comprehensive protection against advanced ballistic and hypersonic missile threats might be a struggle, says Babych, who’s a partner at Aequo in Kyiv. ‘More importantly, any visible fragmentation within the Western alliance sends a clear signal to Russia: prolong the war and raise the stakes,’ she says.

The threats made by the US in regards to Greenland, combined with the country’s recent arrest of the Venezuelan president, Nicolás Maduro, in order for him to face criminal charges – to which he has pled not guilty – and its strikes against Iranian nuclear sites in 2025, raise concerns around the readiness of the US to use military action, and the message being sent to other major powers.

‘The US has always given itself a lot of latitude to bend the rules. Still, it mattered that the world’s most powerful country supported norms against redrawing borders by force and gunboat diplomacy. Now the US is embracing revisionism in word and deed. It can only be a blow to the system,’ says Pomper.

Together with Russia’s invasion of Ukraine and China’s militarisation in the South China Sea – to talk only of major powers – the prohibition on the use of force appears to be slowly eroding. Though all of these situations are different, they have in common the underlying notion that sovereignty is an object that can be bargained over. Without real consequences, ‘might makes right’ could become the dominant consideration in international disputes. ‘Ultimately, replacing legal and diplomatic processes with geopolitical pressure risks normalising a power-based approach to territorial disputes – with consequences that extend far beyond Greenland,’ says Babych.

The prohibition on the use of force has also been violated in other conflicts, emphasises D’Alessandra – who’s also a non-resident scholar at the Carnegie Endowment for International Peace in Washington, DC – for example, in the recent tensions between India and Pakistan.

‘If major powers treat international law as optional, other states will draw the lesson that strength, not rules, governs security, hastening [the advent of] a world in which coercion replaces law, alliances become transactional and the risk of miscalculation and armed conflict rises sharply,’ says Jonathan Hafetz, an officer of the IBA Human Rights Law Committee.

Interstate conflicts have become increasingly common since 2016, with 2024 seeing the highest number of state-based armed conflicts in over seven decades, according to the Uppsala Conflict Data Program.

As shown by Europe’s response to America’s threats involving Greenland, it will be up to coalitions of ‘middle powers’ – in the words of Canadian Prime Minister Mark Carney – to hold powerful nations accountable and impose real consequences for any violations of international agreements created in the post-war era.

‘There is no question that, without the US on board, upholding accountability for egregious international law violations will be more difficult. It will be imperative for cross-regional coalitions to come together to reassert these commitments in what is, today, an ever-more challenging global environment,’ says D’Alessandra.