In January 1942, with most of continental Europe under Nazi control and Allied victory a distant prospect, representatives of Britain, its dominions and nine European governments in exile met at St James' Palace in London.
They did so to declare that war criminals would be "sought out, handed over to justice and judged" and that doing so was "among their principal war aims".
When that declaration was made it seemed "like pie in the sky thinking, completely hopeless, no chance", Professor Philippe Sands, the human rights lawyer and QC, told the Telegraph.
Instead, it formed the basis for the Nuremberg and Tokyo Trials of 1945 and the creation of what we call international law.
In the decades that followed, however, as the world split into opposing Cold War camps, the idea of fair and impartial universal law receded.
Almost five decades after Nuremberg, with the Cold War over but Europe again facing the horrors of genocide and crimes against humanity on its soil, new life was breathed into the concept.
When, in 1993, the intention to go after Yugoslavia's war criminals was announced, it seemed absurd. Jeremy Bowen, a war correspondent in the Balkans, told the BBC on Monday: "All of us journalists thought, well, that's a load of rubbish. It's not going to happen, is it?"
He went on to give evidence at four separate trials at the International Criminal Tribunal for the Former Yugoslavia, an organisation that would have in the dock war criminals right up to and including Slobodan Milosevic, the former president of Serbia.
In the intervening years, there have been a smattering of further successes, with the Special Court for Sierra Leone convicting Charles Taylor, a former Liberian president, in 2012, and Sudan's alleged war criminals finally beginning to face the permanent International Criminal Court (ICC) this year.
And yet, with horrific evidence emerging across Ukraine of Russia's apparent crimes, the concept of international law is facing another key test.
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As in 1942 and 1993, the intent to go after Russian war criminals has already been declared with US President Joe Biden calling for a trial and the ICC beginning to collect evidence.
Yet there are innumerable complications. As a permanent member, Russia wields a veto on any Security Council action. It has also never been a member of the ICC.
Add in that such a trial cannot happen in absentia, and the inescapable conclusion is that the world will have to wait for Vladimir Putin to fall for him to face justice.
Even then, a major difficulty would lie in proving that Putin bears the ultimate responsibility for specific war crimes.
"The task of the prosecutor will be to show that there is a plan, which goes right to the top," said Sands, "If Putin were in the dock, he would say, 'I ordered them to follow the Geneva Conventions and it was wayward officers on the ground who didn't".
The answer to both problems may lie in Nuremberg.
The key crime underpinning that tribunal was that of "crimes against peace", a concept created by a Soviet jurist, Aron Trainin, and now known as the "crime of aggression".
"It's the one that sat at the top of the pyramid because everything else followed from the actions that were taken in waging a war that was manifestly illegal," said Sands.
Proving such a crime, in the words of Geoffrey Robertson, QC, who served as a judge for the Sierra Leone tribunal, would be simple. "He's guilty, obviously, and that won't require much evidence."
It is for that reason that Sands and others are pressing for the creation of a special international tribunal outside UN control but working with the ICC, to try Putin and his followers.
While it would still require the Russian president to appear in person, its work could begin immediately and an indictment produced in a matter of weeks, argued Sands.
That, he said, could "peel away the doubters in the camp around Putin" and accelerate his demise by offering them the carrot of immunity, just as the Americans did with Karl Wolff, the SS general, in 1945.
The reality remains that it could be years or decades before Putin faces a courtroom.
Yet preparing the grounds for his trial still matters, both for pragmatic reasons and more high-minded ones.
One of the key reasons that Milosevic, Radovan Karadzic and Ratko Mladic ended up at The Hague was because Serbia's reacceptance into the international community required it. Likewise, Russia should remain isolated until it hands over its war criminals.
Beyond that, taking on a giant like Russia would reinvigorate international law and send chills down the spines of autocrats across the world.
As a former central European president put it to Sands: "We've always thought that international tribunals were for little, weak countries. What a good thing it would be if it could also be used for one of the powerful ones."