For centuries, Britain and France have been pivotal players in shaping global events, their influence stretching far and wide since the Middle Ages.

However, a senior French civil servant recently remarked that the dynamics of global power are shifting dramatically, leaving both London and Paris on the periphery. For the first time in hundreds of years, these once-dominant nations find themselves sidelined, watching as bigger powers make decisions without their involvement.

The military prowess of the United States, China, and, to a lesser extent, Russia has positioned them as the primary actors on the world stage. In contrast, Western Europe, once the epicenter of international authority, has allowed its influence to wane.

This decline is partly due to a long-standing assumption that America would always provide protection, footing the bill while doing so. Such complacency has rendered Europe ineffective in the current geopolitical landscape.

Back in the 17th century, Louis XIV of France had a Latin motto engraved on his army’s cannons: “Ultima ratio regum,” or “the king’s final argument.” These powerful weapons served as a definitive statement in diplomatic matters.

No matter the treaties or accords negotiated, ultimately, brute force has consistently been the deciding factor in international relations. From ancient tribes to contemporary superpowers, the side wielding the greatest strength dictates the balance of power. The “king’s final argument” invariably prevails.

Donald Trump appears to understand this. He and his MAGA team are revelling in America’s superior force. By overthrowing Nicolas Maduro, Trump has demonstrated his conviction that the US shall do as it chooses across the American continents – a truism that every emperor in history would have understood before him.

Sir Keir Starmer has, at the time of writing, not even been granted the basic courtesy of a phone call to the US President. He is being kept humiliatingly on hold

Donald Trump and his MAGA team are revelling in America’s superior force

These two vast landmasses, bisected by the Panama Canal, are Trump’s ‘sphere of influence’, a phrase from 19th century power politics that sums up his foreign policy thinking. He averred in recent days that Colombia’s president had better ‘watch his a**’, lest he find himself spirited in the dead of night to some jail cell in Colorado.

Trump makes it plain, too, that he includes Greenland in his sphere of influence – and perhaps Canada. One is historically part of the kingdom of Denmark, the other is a Commonwealth country whose head of state is our own King.

Trump’s homeland security adviser Stephen Miller crudely declared on Monday: ‘Nobody’s going to fight the US over the future of Greenland’, reflecting the White House’s confidence that no other country, and especially no European country, would dare challenge America’s military dominance.

This may be uncomfortable for European leaders, but the facts are inarguable. The ‘rules-based international order’ had one rule, or perhaps two. America set the rules. And, by and large, it made them up as it went along.

Sir Alex Younger, the former head of MI6, revealed on Monday that Whitehall, too, understands this new, highly volatile international order. He told BBC Radio 4’s Today programme: ‘We see, essentially, the world now governed by the idea that might is right and that strong men presiding over spheres of influence – and tolerating each other’s activities within that sphere but dominating their own back yard – is the basic operating unit of the world. And I think Donald Trump embodies that.’

Quite so. History, by some readings, is nothing but an endless seesaw between outbreaks of war and efforts at peace. As the Greek historian and general Thucydides famously put it: ‘The strong do as they can, while the weak suffer as they must.’

The Roman empire expanded with overwhelming military might, enforced, often for centuries, by peace treaties. The Treaty of Westphalia in the 17th century created the conditions for modern European nation states after the Thirty Years’ War.

After the Napoleonic wars, in 1815, the Second Treaty of Paris lasted for nearly a century until the outbreak of the First World War in 1914. And following that apocalyptic slaughter, the League of Nations was established to prevent a second global war. It failed. After 1945 came the United Nations and Nato.

All efforts at establishing international peace have one thing in common: eventually they fell apart. Nato is still intact on paper, but it has been gravely damaged by Trump’s vacillations over Ukraine and many observers believe it cannot continue in its present form.

This recurring breakdown of order appears to be a historical inevitability and, as a general rule of thumb, the time it takes to happen is between one and two human lifetimes. During that period, peace is usually underpinned by fear as much as by altruism. Both the governing elite and the population at large appreciate how terrifying and costly war is.

But in the 21st century, most British people have forgotten that visceral fear of war. Anyone who remembers the Second World War in any detail is likely to be in their 90s. Certainly our leaders, who have allowed our military defences to dwindle to a dangerously low ebb, are far too young. They don’t really believe the worst could happen, despite the experiences of our ancestors.

After all, doesn’t ‘international law’ mean that disputes are decided by sober-minded judges in clean, modern capitals? Don’t the flags fluttering outside the United Nations building in New York mean that countries have turned their spears into ploughshares?

Some world leaders do understand the cold currency of power. Vladimir Putin calculated that he could invade Ukraine in 2022 because he anticipated a quick and easy victory, whatever ‘rules’ America had supposedly set.

Trump’s negotiating position with the Kremlin, four years into that conflict, has been seriously undermined by his actions in Venezuela. Putin will now reason that he was right: the White House has no real moral objection to Russian warmongering, and the rules-based international order was a fiction.

In the same way, whether or not China one day attacks Taiwan will not depend on some post-1945 liberal ‘order’. China routinely breaks international law – it lies, steals and enslaves at will. 

The only factor that will determine whether China mounts an invasion is whether China believes it can succeed in doing so at reasonable cost. In ousting Venezuela’s president, I suspect that Trump has only reminded President Xi that the strongest actor makes the ‘rules’ – and thus made any future invasion more likely.

Global powers, then, are less constrained by the rule of law today than at any time since the end of the Second World War. But what makes matters far worse is that Britain and France have less leverage than at any time in the past 500 years.

The UK appears to have no say at all. Sir Keir Starmer has, at the time of writing, not even been granted the basic courtesy of a phone call to the US President. He is being kept humiliatingly on hold. There could be no more pungent proof of our weakness. And make no mistake, this is weakness of our leaders’ own creation.

As a lawyer long before he was a politician, Starmer regards international law as the ultimate safeguard. It is his fundamental worldview – the basis of his entire philosophy, in so far as he has one. This blinking individual cannot grasp one eternal truth: that rules and treaties mean nothing when powerful men decide to break them. 

• Professor Robert Tombs is the author of The English And Their History, published by Penguin.