Yet another east European tragedy is unfolding before our eyes. We have watched this movie for more than 80 years. In 1938, Czechoslovakia was abandoned to its fate by Neville Chamberlain at ‘Munich’. In 1945, at the Yalta conference, it was Poland’s turn — and the eastern half of our continent lost to Soviet domination. Then the Soviet invasions of Hungary in 1956 and Czechoslovakia in 1968, followed in 1981 by a ‘state of war’ in Poland. ‘Goodbye to all that’ we naively thought after the end of the Cold War, but in 2008, Vladimir Putin’s Russia seized chunks of Georgia. Then came 2014: the Russian dictator annexed Crimea from Ukraine and orchestrated armed rebellion in those easternmost parts of the Donetsk and Luhansk provinces which, on Monday this week, he effectively made a part of Russia. 2014 was the turning point at which the West failed to turn. A low-intensity armed conflict has been going on in those regions for eight years now, with more than 14,000 dead, but we in the rest of Europe have kidded ourselves that we can carry on as usual. That’s just ‘eastern Europe’ far away over there — nothing really to do with us. Our reward is to stand on the verge of what could be the largest war in Europe since 1945.

There is Munich and there is ‘Munich’. In the beautiful German city last week, the Munich Security Conference — an annual summit of mainly western political and security elites — was trying to work out how to avoid another ‘Munich’, meaning appeasement of a dictator by concessions that only encourage him to take more. In the gilded conference rooms, European and North American leaders outdid each other in proclaiming that they stood shoulder to shoulder; that any Russian invasion would meet with a co-ordinated barrage of sanctions. But in the bar and coffee lounge, we privately speculated whether that unity would hold if Putin launched less than a full-scale invasion.

I made it back to England just before the worst of the recent storms, which strangely echo the geopolitical climate. Then on Monday evening came that terrible rant by Putin. Do catch up with it on YouTube if you haven’t seen it already. The shocking thing was not just his announcement of the recognition of the ‘People’s Republics’ (familiar misnomer) of Donetsk and Luhansk and deployment of Russian troops there. It was also his almost unhinged manner, bitter fury and wild claims, such as that the ‘puppets’ of the West now ruling in Kiev would develop ‘weapons of mass destruction’. Gone was the calculating practitioner of realpolitik we have known for many years, and at least could rely on to pursue his imperial ambitions with some degree of rationality and realism.

One of the most gripping events in Munich was a ‘Ukrainian lunch’. Among the speakers was Anne Applebaum, who among her claims to fame is, like me, a former foreign editor of The Spectator. Asked what the West should have done earlier to help Ukraine, she said it should have done more to equip that sovereign country to defend itself. I think that’s exactly right. I made the case for more defence assistance to Ukraine in a Guardiancolumn seven years ago, as Russian troops moved into the Donbas for the first time. Much talk of ‘irresponsibility’ and ‘warmongering’ followed. What say those critics now?

I am not, to put it mildly, a fan of Boris Johnson. But he made an excellent speech at the Security Conference. We can’t permit a new Yalta, he said, and must contribute to preserving ‘our continent’s security’. Yes, that’s right, our continent. Now the PM has to put his money where his mouth is. Or rather, put the Russian dirty money swirling around London where its real owners can’t use it.

There can be no ‘Remainers’ or ‘Leavers’ when we face together an existential challenge like this. Indeed, the cross-party unity and robust determination in Britain has so far been impressive — and much appreciated by the Ukrainians I talk to. The real question is whether we can keep the broader unity of the West, as promised on that gilded stage in Munich.

For me, the most moving moment of the week came at the Ukrainian lunch, when I sat next to a young Ukrainian MP who had recently studied at Oxford. Informed, sharp, elegant, she had lived all her life in a largely free Ukraine, from where she had travelled and studied in a free Europe. Now she was going back to a homeland that might any day face a brutal invasion. We in the West thought we had put those bad old times of ‘Munich’, ‘Yalta’ and war behind us. How wrong we were.