This opinion piece was originally published in the Telegraph on 29th March 2026, here.
When the British Foreign Secretary Lord Castlereagh arrived on a freezing European continent on New Year’s Day 1814, he carried with him instructions from the Cabinet about the peace he was tasked to negotiate. Napoleon was on the run after his disastrous march to Moscow and the Sixth Coalition was taking shape to finally bring an end to French dominance of Europe.
Britain did not have an army that could match those of the major European powers. But it could combine its naval and financial power with deft diplomacy, and bring enough force to bear on critical regions like the Spanish peninsula where it bled out French forces, resources and morale.
After his defeat, Napoleon viewed Castlereagh and the British approach to building a post-war order as an inconceivable absurdity. Why had Britain, he wondered, not sought to grind France into the dust and remove from it all the gains that it had achieved after more than two decades of war?
The answer was that Britain did not seek dominance in Europe. Nor was it motivated by vengeance. It sought balance, equilibrium and order. It did not want to replace French dominance with a free hand for Russia. So, not only was France allowed to stay within its 1793 borders, but central Europe was also strengthened via Prussia and the Low Countries. What is more, all the great powers were to work together in a new system of Congress diplomacy whereby their disputes and dilemmas were to be settled by practical diplomacy and informal arbitration.
This order was by no means perfect. Within a few years, Castlereagh became concerned that the great powers were too willing to interfere in the sovereign affairs of smaller nations based on “abstract principles” that went beyond the terms agreed at the Congress of Vienna. Later generations complained that the Congress system stifled the emergence of liberal constitutionalism and national aspirations, leading to later explosions in European affairs and playing its part in the origin of the First World War.
At the Paris Peace Conference of 1919, Woodrow Wilson repudiated any “whiff of Vienna”, rebutting the historically-minded British diplomats who sought to learn from the past. But there is a reason why some of the great strategic thinkers of the 20th century, like Henry Kissinger, studied these efforts carefully and sought to learn the lessons – good and bad – about how to establish an element of order, rules, and norms as an antidote to the ravages of instability, anarchy and war – including in the nuclear age.
For more than 200 years, one of the central features of British diplomacy has been its ability to look beyond transactionalism and a narrow view of the national interest. Indeed, British grand strategy since the Napoleonic Wars has contained within it the goal to construct an international order, starting with but not restricted to Europe, in which a balance of power was the basis, but in which states in the system had the means to redress and resolve their disputes with measures stopping short of war.
There was, and there remains, a strong degree of self-interest in that story. But it was not simply a guise to ensure the preservation of an Empire or a global trading system which suited British interests uniquely. There was also, particularly at the conclusion of the two world wars, a genuine and deep-seated internationalism shared by both the political class and much of the electorate. Thus, Britain played a leading intellectual and architectural role in the two international orders built out of the ashes of those two conflicts.
The first effort, ultimately, was a tragic failure in which a surfeit of idealism – grand ideas about a parliament of nations, disarmament and international law – had been too far detached from both the tragic realities of geopolitics and unwilling to confront those hostile to that order through collective security. The second, the creation of the 1945 order, was a success, underwritten by American power but incorporating an ever-increasing plurality of nations under its umbrella.
It is with good reason that we celebrate the post-1945 order – an achievement that Jim Mattis, as secretary of defence in the first Trump administration, told his boss was the “greatest gift of the greatest generation”. It is with good reason that those charged with the stewardship of British foreign policy share a particular anxiety about the weakening of that international order which we are witnessing today.
And yet, there is a real danger that Britain is not prepared for the new world that is emerging before us, because it is too attached to a noble, nostalgic but partial and therefore misleading version of the past. This is an approach that risks replicating the mistakes that followed the erosion and collapse of the post-1919 order rather than learning the true lessons of order-building in 1815 and 1945. That is: a form of foreign policy in which high legalism is treated as the lodestar of our foreign policy, and in which our principal energies are focused on a rickety superstructure, with insufficient attention given to the things that truly make a functioning international order work.
We are both academics – one in international law, the other in history – who have been close to or directly involved in government. We have taught and written about the international order and have also engaged with it professionally for many years. One of us has just returned from the Peace Palace in The Hague, where he appeared for Rwanda in its dispute with the United Kingdom under the Migration and Economic Development Partnership. The other has written books about key figures who helped build the orders in 1815 and 1945, from Castlereagh to Clement Attlee. It is from this vantage point that we approach the current debate on the state of the international order.
There is no denying that the international system is undergoing a profound upheaval: wars in Europe and the Middle East; cooperation between great powers at a very low ebb; multilateral institutions like the UN or the WTO ever less relevant; and alliances like Nato looking more fragile. But we fear that much of the current debate is making it difficult for Britain to rise to the challenge of the present moment – as it did in the past.
Our concern starts from the way that the idea of a rules-based order is treated as an almost theological abstraction, as a God-given gift from which dissent cannot be contemplated. By this argument, the answer to our current discontent is to make fidelity to international law the organising goal of our foreign policy and the premise of every decision we take. This risks creating an imbalance in our foreign policy in a world where ever-fewer states share this approach.
Importantly, it is an approach that goes way beyond the astute Chilcot checklist in which international law is treated as one of 10 critical points to consider in the making of national security decisions. Yet those who may question this prioritisation – international law crowding out all other considerations – have been accused of being followers of the Nazi theorist Carl Schmitt, as somehow willing to give up on international law in favour of might over right.
The danger is that we end up as curators of an old system rather than active participants in a new world in which power is being more nakedly asserted. It is by a combination of tenacity, risk-taking and creativity that we have made ourselves present at the creation of previous international orders. If Britain is to have any say in the shaping of a future one, it cannot do so based on an abridged or ideological version of what has served us so well in the past.
The heritage of British foreign policy that we seek to invoke, one could call it Churchillian or Bevinite. It is definitely not an argument for might rather than right – an absurd and tendentious proposition designed to shut down debate – but a recognition that what is right does not transpire in international affairs simply by appeals to universal principles and laws.
Rather than Schmitt’s dark philosophy or Immanuel Kant’s ideas of “perpetual peace”, the tradition we invoke is fully in keeping with the ideas of the founding father of international law, Hugo Grotius. It was Grotius who made the case for a law of nations in a Europe divided by wars of religion. That project could only succeed, however, if it did not rest on universal theories or grand abstractions, but it remained attentive to the practice of statecraft, and fully conscious of the tension between moral aspiration and political reality.
The real story of the order built in 1945 reflects that more practical tradition, including direct invocation of the Grotian spirit. As recounted in Andrew Ehrhardt’s new book, A Grand Strategy of Peace, Britain played a central role in the creation of the UN system. But it was not simply the triumph of Wilsonian idealism that was the key to that peace, so much as the ability to craft it upon the basis of a great power peace.
The 1945 order was, in essence, a rules-based order alongside a power-based order. The legal framework helped protect the sovereignty of medium and small powers, but the burden of maintaining collective security – and of acting pre-emptively against threats to international peace and security when required – fell upon the great powers.
As such, they would use their own military power but also draw on the forces that all UN members undertook to place at the organisation’s disposal under Articles 43 to 45 of the Charter. Meanwhile, Article 47 established a Military Staff Committee, composed of the Chiefs of Staff of the five permanent members, to provide strategic direction. Articles 53 and 107 – seldom mentioned these days – preserved the possibility of enforcement against any State that had been an “enemy State” in the Second World War in the event of the “renewal of aggressive policy” by that State.
Even in this system of collective security, the inherent right of self-defence was considered sacrosanct and was enshrined in Article 51 of the UN Charter. The language of this provision appears to exclude anticipatory action. Yet, unless this language is understood within the wider security architecture, we are left with a completely ahistorical and distorted picture of the 1945 post-war order.
No one in San Francisco imagined they were signing up to an international order that would legally oblige them to wait for a Fourth Reich to cross the Rhine before taking action – not to mention one where they would have had to sit and watch as that Fourth Reich acquired nuclear weapons. Indeed, today it is often forgotten that this order was conceived in a world where nuclear weapons did not yet exist. The UN Charter was signed three weeks before the Trinity Test in New Mexico.
In some respects, the crisis of the 1945 order began at conception. Even the US and Britain were divided by a fundamental difference: the future of the colonial empires. With the Cold War, it soon became clear that there was no concert of Great Powers capable of ensuring international peace and security: the legal architecture would remain in place, but collective security could only be enforced by coalitions of the willing, often outside the UN system, such as the Nato alliance.
Accusations of breaches of the Charter’s principles were routinely exchanged during the Cold War, with each side keen to be viewed as rule-abiding. Yet only a very credulous observer would conclude that the relative avoidance of war, such as it was, flowed from rules such as the legal prohibition on the use of force. When the world stood on the brink of a third world war during the Cuban missile crisis in 1962, catastrophe was averted not by law, but by a last-minute accommodation between the great powers of a kind familiar to nineteenth-century diplomats.
What followed in the 1960s and 1970s was an attempt, by statesmen such as Kissinger, to build a new security architecture – not as ambitious as that which had briefly seemed achievable in 1945, but very important nonetheless. Its main elements were the bilateral agreements between the US and the USSR to limit nuclear arsenals and reduce the risk of nuclear war by accident or error; and the multilateral treaty regime on weapons of mass destruction like the 1970 Nuclear Non-Proliferation Treaty and the 1972 Biological Weapons Convention. It reflected the reality of power and was backed up by the credibility of force.
And then, from the 1990s, the international order changed its face again. With the end of the Cold War, international law experienced a surge of ambition and expansion: from the World Trade Organisation to the International Criminal Court; from the proliferation of international human rights law to a web of treaties protecting foreign investment. International adjudication grew at a rapid pace.
As this process unfolded, a new conception of international law took hold in the Western liberal imagination: international law began to be seen as the vehicle for a comprehensive moral and political project, with international institutions as its principal agents. The result of this ideological turn was a form of international law that was rhetorically confident but increasingly detached from statecraft and less capable of self‑correction. Buttressing this ideological turn was a Whiggish conviction that the role of international law was to carry humanity along the right side of history. A new set of apostles and interest groups appointed themselves as the protectors of this reconceived international law.
While some had been calling for moderation in the face of the growth of international law after 1989, this new ideology demanded an ever more activist and expansionist approach. It is this philosophy that helps explain why the European Court of Human Rights, among others, has felt compelled to adopt increasingly bold interpretations – developments that have in turn provoked political backlash.
So, in truth, many of today’s appeals to the sanctity of international law go well beyond the order of 1945 and often say more about an “end of history” mentality of 1989.
Indeed, what is really being sought is not a return to the hard-nosed and hard-fought international order of 1945 but rather the reassurance that the particular conception of international order that took hold in the liberal imagination from the 1990s – one built around ever more progressive interpretations of rules and the illusion that power could be tamed into irrelevance – can be restored.
As we look around us, however, the principal challenges facing British statecraft go well beyond matters of law alone. Can deterrence be achieved on current levels of defence spending? What is our message to Eastern European allies that have chosen, for fear of Russian invasion, to withdraw from treaties banning anti-personnel landmines and cluster munitions – treaties to which, as work by Policy Exchange has noted, the UK still subscribes? The open-ended nature of the war in Iran, which drags on with profoundly troubling implications, will not leave us in the situation of being able to revert to a happy norm.
What do we say to partners in the Gulf, worried about their future security, for whom our highly restrictive legal approach to military targeting in the current conflict seems so remote from both past British practice and the reality they now face?
To be clear, throwing the baby out with the bathwater would be the worst of all worlds. Those who take any relish from the erosion of order, and its associated norms, are entertaining a deeply misbegotten worldview. Many of the old international laws and rules continue to form the basis of our economic well-being and ability to achieve successful diplomatic outcomes. But they require adaptation rather than trenchant restatement – still less the elevation of a 1990s ideology over our national interest.
Above all, they require a proper understanding of our history that recognises the practical, Grotian tradition and the spirit of people like Castlereagh or Bevin. If that tradition is displaced by an ahistorical and overly idealised view of international order, Britain will fail to meet the demands of the present moment.
Professor John Bew is former No 10 foreign affairs adviser is a professor of War Studies at King’s College London. He is a senior fellow at Policy Exchange
Lord Verdirame KC is Professor of International Law at King’s College London and the recipient of Policy Exchange’s Grotius Prize 2026
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