Consider a very British scenario. A beloved monarch has just died, and the stability they embodied is starting to fade. At home, there is growing industrial conflict between capital and labour, and growing constitutional conflict between secessionism and Unionism. Externally, too, the world is becoming increasingly hostile, defined by escalating rivalries and rearmament in Europe and Asia. A recent Russian war demonstrates the possibility of an era of armed conflict. Faced with these competing demands, the British state starts to groan. Suddenly, everything is at stake.

This was the reality for Britain at the close of the Edwardian era, and it echoes our fraught position now. The Edwardians responded, as Aaron Friedberg has noted, by trying “everything they could think of” to “shore up their position without forcing them to spend more money”. A touch of Edwardian prudence would be similarly helpful today.

Across Europe, a strategic shock lies dormant in the shifting structure of world politics — namely, a partial US withdrawal from Britain’s wider region, and the realisation that locals must shoulder most of the security burden themselves. Faced with such a predicament, the British Government should revive a strategy that dates back more than a century: an Entente Cordiale with the other leading military states of Europe, such as France and Poland.

In some ways, circumstances today are milder than at the turn of the 20th Century. There is no equivalent of the German Kaiserreich, threatening to seize hegemony over the region, while Britain then was close to civil war over Ireland and the constitution. In other ways, however, the situation is worse. Nuclear weapons make even a depleted, thwarted Russia an enduring problem, a giant North Korea on Nato’s frontiers. Britain is also no longer the world’s leading state, measured in naval reach or financial sinew. It lacks the imperial resource base and the reserve currency of a century ago. And there are now forces loose in the world, shifts of wealth and power, that Britain cannot extinguish.

In turn, this means the United States will be increasingly unable and unwilling to do the heavy lifting as Europe’s security provider. British defence planning, like its statecraft, long worked on the assumption that the American colossus would underwrite it. A US forward presence in the form of continental garrisoning was a given, as was the ultimate assurance of extended nuclear deterrence under an American “umbrella”. The issues that divided strategic minds — the balance between continental and domestic commitments; the division of labour within Nato; the trade-offs between flexibility and specialism — rested on the assumption that America would stand sentry.

But as China’s bid for primacy in Asia forces Washington to focus on one theatre above others, this assumption has become increasingly unsound. Even if American politics is led by European-friendly primacists for the next generation, and even with a rear-guard effort by the foreign policy establishment to resist, new realities will bear down upon Washington and force it to prioritise the largest, richest near-peer adversary in its history.

This won’t be immediate. The prospect of a drawdown is clouded by Washington’s recent partial re-pivot to Europe following Russia’s invasion of Ukraine. But the contest for primacy in Asia is intensifying, and will soon assert itself at the top of America’s agenda. Only this month, China conducted the largest simulation of a naval blockade against Taiwan, the epicentre of the US-China struggle. This is part of a wider escalating rivalry, with Washington legislating to kneecap China’s microchip imports.

The scale of the challenge to America’s pre-eminence in the Indo-Pacific region is likely to exert a near-gravitational pull on its attention. It will increase the demand on its diplomacy, its military power, its industrial base and presidential time. Americans will be increasingly reluctant to maintain a global posture. Something will have to “give”. And the likeliest candidate will be America’s commitment to wealthy allies in a region where its competitor is 10 times smaller in GDP terms than China, and cannot hope to overrun or dominate the continent. While the US is likely to retain a balancing “hand” in Europe, it will become averse to playing Uncle Sucker.

Faced with this change in priorities, it would be foolish for British or European policymakers to just muddle through and wish away the problem. Even within alleged “special” transatlantic relationships, Washington, like all great powers in history, has unilaterally imposed ruthless policy change, to its allies’ disfavour, with little warning. Recall President Harry Truman’s about-face in the early post-war period, terminating the Lend-Lease Act which transferred war supplies to any nation vital to America’s defence, ending talks over nuclear cooperation, and imposing fixed dollar-pound convertibility, which caused a currency and dollar/​gold reserves crisis in Britain.

It would also be imprudent to imagine that the US will delay its withdrawal because the proxy war in Ukraine is comparatively “cheap”. A diversion of 20,000 military personnel into Europe is not cheap, strategically, especially as it also diverts precious air, naval, logistics, surveillance and reconnaissance assets. Neither is it cheap to deplete weapons and munitions stocks to the point where it exceeds capacity to reproduce it.

Instead, given the difficulty of its senior ally sustaining commitments in two theatres at once, it would be wiser to anticipate the shock, and enter into a form of security cooperation, recast from history. This would be an informal channel of cooperation between the leading military states of the region — Britain, France and Poland — that would collectively negotiate the strengthening of capability in the neighbourhood independent of the United States. It would proceed on the common assumption that European powers will soon be forced to shoulder far more of the burden of their own defence, and will have to develop the ability to operate independently of their traditional guarantor. It would work both on a diplomatic level and between military staffs.

Ententes have the benefit of offering the advantages of informality and flexibility. A new formal organisation would be too long and complex to set up, raise anxieties about the supplanting of existing institutions, such as the EU, and impose credibility pressures to live up to. A less conspicuous Entente, by contrast, away from the glare of summits, would facilitate bargaining over hard capabilities, intelligence, interoperability and defence resilience in general (including cyber, stocks of materiel and supply chains). It would be austere in its political focus, centred on a common concern, countering any hostile attempt to weaken Nato or dominate the region while steering clear of ideological differences over liberal values that could strain ties.

In political terms, this should all be achievable. A new Entente would align with and give shape to France’s call for “strategic autonomy”, but in a more practical and less performative fashion. It would soften the message of autonomy, shifting it towards burden shifting, but with the welcome benefit that it would give France a greater say in European defence. In Warsaw, meanwhile, the country most anxious about the impact of American drawdown, it would shift the focus away from France’s dalliance with neutralism over China, and towards hard commitments towards defending Europe. And for Britain, an Entente would mitigate the security disadvantages of Brexit, by inserting it more centrally into a dialogue over collective defence that does not presuppose common EU membership.

Perhaps most important, with joint military planning the Entente, like its precedent, would help its members neutralise wider points of friction. While in the Edwardian era that was an imperial bargain over respective spheres in Africa and the Middle East, now it would focus on easing post-Brexit quarrel where the three countries most collide, namely over the division of labour over borders and migration.

Of course, this new Entente would probably create friction with the United States. That friction, however, would surely be a price worth paying for all sides. It would meet America’s traditional request that its allies shoulder more of the security burden. And as the US becomes increasingly preoccupied with the Indo-Pacific, it will find the Entente actually facilitates its efforts in the Asian theatre; it will free up its people, money and equipment to concentrate power where it matters most. As America prepares to downgrade its European profile — for the sake of the entire Western alliance, Europe should be ready.