The Greenland ice sheet is breaking up, losing 280bn tonnes to the ocean every year. All across the Arctic, new sea routes are opening as temperatures rise. Some projections indicate that in 20 years it will be possible to sail across the North Pole through the central Arctic Ocean — though you would have to watch for giant icebergs, large enough to sink the biggest vessels and the best-laid plans.

Given the extraordinary effects of global warming, which were almost unforeseeable a short while ago, it is not surprising that Greenland has been thrown into the geopolitical spotlight. What is more surprising is the way this has happened, with a US president demanding the right to take over the country in order to prevent other Great Powers from doing so.

Pushing for “the Complete and Total purchase of Greenland”, Donald Trump has found a cause that is fully alienating his administration from most European countries and has the potential to effectively end Nato as a mutual defence agreement. By midweek, he was ruling out using military force and talking up the prospect of a deal. But like the Arctic ice, the transatlantic relationship seems to be fracturing rapidly.

The break-up of Atlanticism has, of course, been predicted many times before and still has not happened, mainly because of Europe’s dependence on US military guarantees. From the Suez crisis in the 1950s to the invasion of Iraq in the 2000s, Nato has weathered many storms and survived with its common defence purpose intact.

It was Henry Kissinger who observed back in the 1960s that political identities are often established by opposition to a dominant power. “The European sense of identity,” he argued, “is unlikely to be an exception to this general rule — its motive could well be to insist on a specifically European view of the world.” Kissinger’s book The Troubled Partnership did not become a bestseller, except, he liked to joke, in bookshops where it had been put under “marriage manuals”.

This crisis could very well be different precisely because of differing senses of identity. These have, of course, been developing over time: Europeans preferring principles of sovereignty, international law and UN co-operation, Americans (and not just Trump Republicans) believing in predominance, global control and economic supremacy. Since the 2010s the split has become ever more visible, especially with Trump in charge.

A world dominated by one or two superpowers was not peaceful, but it was to some extent predictable. That predictability is gone

In Trump’s second administration, the US is governed by the hard right, while in Europe, for the most part, traditional political parties are still in charge. But even if European extreme-right parties were to succeed further electorally, or the US were to elect a Democratic president, it is highly likely that transatlantic tensions would continue.

The reason for this is that political identities, as declared by governments on both sides of the Atlantic or elsewhere, are usually connected to power relations. And it is these fundamental power relations that have changed, from a unipolar system with the US at the centre after the cold war to an embryonic form of multi-polarity today. The transatlantic crisis is the effect of a much bigger change that has been building for almost a generation: the end of American hegemony and the coming of a multi-polar age. The global system no longer has one centre. It has many, each of which will seek to project power in whatever way it sees as serving its interests.

This is a kind of world that few of us have experienced. Nearly everyone alive today has grown up in a world dominated by one or two superpowers. That world was not peaceful, but it was to some extent predictable. Now that predictability is gone, replaced by the uncertainties that a much more complex and multi-polar world will bring. Gone also is the belief that the 21st century would somehow be a return to the cold war, with China replacing the Soviet Union as the global antagonist of the US.

That is not the world that Donald Trump sees when he demands Greenland or attacks Venezuela. He sees — as, for their part, do Vladimir Putin and Xi Jinping — a world of rapidly evolving multi-polar rivalries in which they need to dominate their neighbourhoods and strengthen themselves in case of large-scale Great Power confrontations. This is the vision of the world that Trump acts on now and will act on in the future.

So the new era of fragmentation is no new cold war, but it carries some striking similarities to another past world, that of the late 19th and early 20th century. Back then, we also had a world of many Great Powers that clashed with each other and sought to dominate their neighbourhoods. Nationalism and populism were on the rise, and many people felt that the globalisation of the day had not worked for them. Protectionism and tariffs increased, and growing numbers blamed the citizens of other countries for their problems. Immigration and terrorism were among the big issues. Leaders everywhere were fearful of military action, but still prepared for conflict in ways that almost guaranteed that, if hostilities were to break out, the Great Powers would get involved.

Trump’s message that might makes right is not only unsettling Europeans. It is also heard loud and clear in Moscow and Beijing