The Polish army fields three divisions, as does Germany’s Bundeswehr. France has two, Romania two, the UK two and the Baltic states could just about scrape together one. As of last week, those are the only forces Vladimir Putin has to consider as he threatens, bullies and cajoles the western diplomatic order into disintegration.

Because from the mouth of Donald Trump came only cowardice.

Trump declined to reiterate any commitment to Nato’s article 5, which mandates mutual defence in the face of attack. He lashed Europe’s leaders about defence spending and then bragged to US troops in Sicily that, as a result of his own election, “money is beginning to pour in”.

While Theresa May could only smile at her shoes, it fell to a shocked Angela Merkel to spell out what Trump meant. “The times in which we could completely depend on others are, to a certain extent, over. I’ve experienced that in the last few days,” she told a party rally. “We Europeans truly have to take our fate into our own hands.”

Behind the scenes, Trump’s diplomats signalled it is not just on defence that the multilateral order is under threat. Trump may, as early as this week, pull the US out of the Paris climate treaty. Even if he does not, his commitment to it will be seen as weak. And his aides refused to include a commitment to free trade in the G7 communique.

The true meaning of “America first” is clear. The Trump presidency will put the interests of American coal, oil and fracking companies first, before that of the planet’s ecosystem. It will place the interests of US-owned car manufacturers first, above those of Volkswagen and Mercedes. And if it comes to a military face-off with Putin’s Russia, America will fight last.

This rip in the global order may last only four years. Or it may snowball.

Either way, it is now rational for both the EU powers and the British government to design a new strategy, for a world where, every so often, the US electoral cycle produces a corrupt, deluded isolationist who can think only in monosyllables.

Merkel’s analysis, if followed to its logical conclusion, must trigger a big change in the economic, trade strategy and security policies of the EU. Her speech should lead Europe to consolidate around its core countries and its core values. If that means yellow-carding Hungary and Poland, whose infractions of democratic rights are now too large to be ignored, that’s fine. Likewise, if the result is a core/periphery arrangement, with the core becoming a fiscal and monetary union, the sooner the better.

Britain, set on a catastrophic exit from the EU’s single market, also faced a wakeup call at last week’s G7. When the UK was the dominant world power, the “perfidious Albion” tactic made sense: playing one European power against another and revelling in their weakness. During the post-1945 era of US dominance, perfidious Albion became a no-cost diplomatic reflex, used mainly by British diplomats to get their way in Brussels. This urge to stand aloof from Europe and divide it where possible is hardwired into the UK’s diplomatic and geostrategic institutions.

Whatever form Brexit takes economically, we need to unwire it fast. Because Trump’s speeches have reshaped the world.

As he shoved minor European politicians in the chest, and tried to crush Emmanuel Macron’s hand, Trump’s security services were playing equally macho games with photographs of bloodstained clothing from the Manchester bombing. The political signal behind that leak was clear: for the Trumpian state, it is the security interest of the US that come first, the priorities of a live anti-terror manhunt in Manchester second.

The xenophobic right in Britain, whose biggest jeers are reserved for the concept of a European army, had better hope one can be formed. Because after Trump’s speech, that’s what we’re going to need to deter the threat of a Ukraine or Crimea situation being created at the EU’s borders.

For British politics, this demand for clear thinking comes at the worst possible time. The Conservative cabinet is full of deluded amateurs. People who fantasise about Empire 2.0; people prepared to reimpose a land border on Ireland; prepared to turn the election into a nostalgic re-run of the conflict with the IRA.

Jeremy Corbyn, although he has left behind pacifism and unilateralism, needs to facilitate the emergence of a new, positive Labour defence and security policy. It should be focused on the real threats – a disintegrating world order and the growing unpredictability of thousands of jihadis in the UK – not just a set of old leftwing nostrums.

The lessons from history are clear. When the US shies away from Europe, as it did between 1939 and 1941, the UK has to function primarily as a European power, even to pursue its own narrow security. As the details emerge of how the Manchester bomber, Salman Abedi, got himself and his bomb to the city, the need for more European cooperation on security will become clear.

In a world as dangerous as this, led by men as dangerous as Trump and Putin, we should need no prompting to exceed the 2% of GDP defence spending target, and to reverse all cuts to police, fire and emergency services. The fact is that Trump has signalled that the current “strategic concept” of Nato, written in 2010, is a dead letter. The major European democracies need to craft a new one. And Britain has to be part of that.