But the answer is not so simple. Nuclear bombs have been dropped in conflict just once, in August 1945, by the United States. The horrific scenes of destruction and human suffering in Hiroshima and Nagasaki — and a death toll estimated to be about 200,000 civilians — provoked widespread condemnation. The theologian Reinhold Niebuhr wrote in the New York Times that the bombings were “morally indefensible”. Even hardened military figures were aghast. “We had adopted the ethical stand common to the barbarians in the Dark Ages,” grieved Admiral William Leahy, the US’s highest-ranking military commander.

Years later, the former Supreme Allied Commander Dwight Eisenhower told Newsweek: “It wasn’t necessary to hit them with that awful thing”. It was a comment that alluded to the military tactics behind the decision, which are separate from the more emotive philosophical debate over the morality of dropping the bomb. What does it mean for it to be “necessary” to drop a nuclear weapon? If it wasn’t necessary, then why did the US government — indeed, why would any government — willingly inflict such pain and suffering on civilians if there was a legitimate alternative path to peace?

The man who made the decision, Harry Truman, gave a lecture in 1959 to Columbia University students about the powers of the presidency. The talk was described as “earnest, good-humoured, and sometimes salty”, and was well-received by the 1,200-strong audience. But during the question and answer session, things took a more serious turn. A student thought it was odd that Truman had skirted over the nuclear question. When confronted with it, the usually good-natured Truman became a touch defensive:

“It was used in the war, and for your information, there were more people killed by the fire bombs in Tokyo than dropping of the atomic bombs accounted for. It was merely another powerful weapon in the arsenal of righteousness. The dropping of the bombs stopped the war, saved millions of lives”.

This is the orthodox view: dropping nuclear bombs saved lives. In this telling, the Japanese were not prepared to surrender, meaning the US and Soviet Union had two choices. They could either launch a land invasion, something on the scale of the D-Day landings in France, in which an estimated million US soldiers alone would be lost. Or they could prevent such a bloody undertaking by shocking the Japanese leadership into capitulation.

Death was not enough. The fire bombings of Tokyo, in which 100,000 people died in one night, had not proved sufficient. Something beyond conventional warfare was needed. Nuclear warfare was, as Truman’s Secretary of War Henry Stimson put it, the “least abhorrent choice”; though the bombs killed hundreds of thousands, even more would have died had they not been dropped.

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The orthodox account depends on a number of key claims, including that the Japanese were unwilling to surrender in the summer of 1945. These claims have since been challenged by “revisionist” historians, who argue that Japan was in fact on the verge of surrender when the bombs were dropped.

The previous summer, Japan had lost Saipan, an island in the South Pacific, to America, meaning its mainland was within range of USAF B-29 bombers. This made Japan highly vulnerable to sustained US attacks from the air. On the night of 9 March 1945, over 300 B-29 bombers descended on Tokyo, inflicting the deadliest bombing raid in world history. After that, the revisionist account goes, the question was not whether Japan would surrender but on what terms.

The revisionists place heavy emphasis on contemporary reports that suggest the Emperor and some (but not all) of his advisers were inclined to surrender, so long as his position could be guaranteed. A month before Hiroshima, Navy Secretary James Forrestal wrote in his diary: “The first real evidence of a Japanese desire to get out of the war came today… [indicating] the Emperor’s strong desire to secure a termination of the war”. A 1946 report by the US Strategic Bombing Survey concluded: “in all probability prior to 1 November 1945 [the planned invasion date], Japan would have surrendered even if the atomic bombs had not been dropped.”

The revisionists believe that the US rushed to use nuclear weapons not because of Japanese intransigence, but because of the Soviet Union. Throughout the war, the USSR and Japan had honoured a neutrality pact. Stalin, however, assured Truman’s predecessor Franklin Roosevelt that three months after victory in Europe was achieved, the Soviet Union would turn its attention to the Pacific and declare war on Japan. Truman and his closest advisers believed that Roosevelt had already conceded far too much to Stalin at Yalta, effectively giving the USSR free rein to dominate eastern Europe. They were not keen for the same thing to happen in Japan.

The first bomb was dropped on Hiroshima on August 6. On August 8, exactly three months after the surrender of Germany, the Soviet Union declared war on Japan. The following day, the second bomb was dropped on Nagasaki. The day after, the Japanese government offered its surrender. The revisionists look at this timeline and intuit that the nuclear bombs were dropped primarily for political rather than military reasons. The US wished to deny the USSR credit for ending the war, which would have given Stalin greater leverage in the post-war settlement.

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These two accounts — the orthodox and the revisionist — are the dominant explanations offered by historians, but they are not the only ones. Some scholars focus on the internal politics of Japan, arguing that the key figures who were ready for peace, not least the Emperor, were poor at communicating their wishes. They were, perhaps, drowned out by the powerful voices who wanted to continue the war. Many in the rank and file of the military were believed to be prepared to fight at all costs. US propaganda, which was racially inflected, tended to exploit the perception of Japan as a “warrior culture”, in which people would choose death over the shame of defeat. It was hard for Americans to discern Japan’s true intentions.

Other accounts suggest Truman was locked into decisions made by his predecessor. It was Roosevelt who had pushed for “unconditional surrender” at the Cairo conference in 1943. And the idea of dropping nuclear bombs on Japan was one Roosevelt had first dreamed up. In September 1944, he and Churchill met at FDR’s estate in Hyde Park, New York and agreed that “when a bomb is finally available, it might perhaps, after mutual consideration, be used against the Japanese, who should be warned that this bombardment will be repeated until they surrender”. Once Truman became president after Roosevelt’s death in April 1945, only one thing could apparently bring about “unconditional surrender”, and that was the bomb.

All of these interpretations offer important lessons to today’s leaders, but that last one is particularly chilling. If dropping the nuclear bomb was not militarily necessary to bring about an end to the war, then Truman opted for a decision that killed hundreds of thousands of civilians in part to save face. Once the US was committed to demanding “unconditional surrender” — for which there was enormous public support — Truman could hardly change his mind and say he wanted a negotiated peace. The new president, who had no political mandate of his own, would risk tanking his own domestic popularity before his term had even begun.

In other words, leaders must avoid making dangerous commitments from which either they or their successors will struggle to back down. Fortunately, in today’s conflict, no one has rashly insisted on “unconditional surrender”. A negotiated settlement is still possible.

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With that in mind, it’s worth considering the vital role of intermediaries in such high-powered conflicts. With the help of a neutral party, could the Japanese peace camp have communicated its position more clearly, so as to assist those within the US administration who might have urged caution? The Japanese saw the Soviets as possible intermediaries, a view that was shattered when Stalin declared war on them. Today, Israel seems to be the go-between, though the nation has been criticised by Western commentators for not condemning Putin.

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At Columbia University, Truman was asked, “With the development of nuclear weapons, do you think the United States would be willing to risk entering a third world war if a small European country in the Nato pact were to be involved in an act of aggression?” His answer was tepid: “I don’t know”. On consideration, he explained that the circumstances were now different, because unlike in 1945, the US was no longer the sole possessor of nuclear weapons: “I don’t think there’s any possible chance of doing what I tried to begin with, when we had absolute control of them, of nuclear weapons”.

This, strangely enough, is cause for optimism. When the US dropped its bombs on Japan, there was no other nuclear power to retaliate. In the intervening years, the threat of mutually assured destruction has seemingly prevented any other country from using such dangerous force.

It’s also worth observing that, while Ukrainians have shown an admirable fighting spirit in defending their nation from Russia, in the eyes of their people the two nations have a lot more in common than the Japanese did with the Americans. There has been no real attempt to use racial differences to demonise the enemy.

There is still a chance, then, that this war can be resolved through conventional methods. Putin is not in the same place Truman found himself in. Putin does not view it as “necessary” to drop a nuclear bomb. It has not yet become Putin’s “least abhorrent choice”. Let us hope it never does.

Truman was nobody’s idea of a great man of history. A small, trim man with neatly parted grey hair, his hazel eyes framed behind thick spectacles, he had a flat, Midwestern twang and a complete lack of stage presence. When Harry Truman walked into a room, nobody looked up. Even if you did notice him, you might mistake him for the man he had once been — not the President of the United States, but a Kansas City haberdasher whose store had gone bust after just two years. A little man, then. A modest man, with much to be modest about. As everybody knew, the S. literally stood for nothing.

What was Truman doing there? The short answer is that he had been extraordinarily lucky. After serving as a captain in the First World War, he had gone into politics, a Democratic party hack working for the corrupt Kansas City boss Tom Pendergast. But when, in the last year of the Second World War, Franklin D. Roosevelt ran out of potential vice presidents, he was persuaded to consider Truman as a compromise candidate. Roosevelt barely knew him — who did? — but he picked him anyway. Truman could barely believe it. He, Harry S. Truman, the farmer’s son from Independence, Missouri, Vice President of the United States!

Then fate took another twist. On 12 April 1945, with his forces fighting their way into Nazi Germany, Roosevelt dropped dead of a massive stroke. Suddenly, unbelievably, Truman was President. When he got the news — he was, naturally, having a drink with his old Senate pals — the colour drained from his cheeks. Immediately he went to see Roosevelt’s widow Eleanor and asked if there was anything he could do to help. Her response spoke volumes. “Is there anything we can do for you?” she said. “For you are the one in trouble now.”

That was two years ago. Now it was 12 March 1947, and the American political elite were looking up at him, and Truman was peering through his glasses at his typewritten text. His voice was as flat and characterless as ever, and as he launched into a detailed description of the political situation in divided, bleeding Greece, the soaring oratory of his charismatic predecessor seemed like ancient history. The haberdasher was in the house, and it was only a matter of time before people started snoring.

But they didn’t. For what Truman said that day was so electric, so momentous, that it arguably had more impact on history than almost any other speech by any other president since Abraham Lincoln. The United States, he told his listeners, was in a new world war — an undeclared war, not of armies but of ideologies. “At the present moment in world history”, he said, “nearly every nation must choose between alternative ways of life”. One was based on individual liberty, free speech and democratic elections. The other, Communism, relied upon “terror and oppression, a controlled press and radio; fixed elections, and the suppression of personal freedoms”.

They all knew that. But what followed was the real surprise.

Truman wanted Congress to give $400 million immediately in aid to Greece and Turkey. It was essential, he said, that neither fell to Communism, and the United States must ensure that they didn’t. And he went further. This would not be a one-off; it must be a general rule. “I believe”, Truman said, “that it must be the policy of the United States to support free peoples who are resisting attempted subjugation by armed minorities or by outside pressures. I believe that we must assist free peoples to work out their own destinies in their own way. I believe that our help should be primarily through economic and financial aid”.

It would be expensive, he admitted. But it was an “investment in world freedom and world peace” — the kind of investment that only the United States could afford. That was their historic challenge, and Harry Truman was not afraid to meet it.

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Today that speech is remembered as the genesis of the Truman Doctrine, when the United States committed itself to the defence of democracy against the advance of Communism. The usual word for this campaign, which never appears in the speech, is “containment”, and that sums it up pretty well. Truman had no intention of going to war against Stalin’s Soviet Union, and was careful to avoid any overtly military provocations. But he was in absolutely no doubt that there were such things as right and wrong; that Soviet Communism was wrong; and that it was his patriotic and moral duty to contain it.

You can probably guess where I’m heading with this. First, though, an illuminating historical side-note. The man who coined the word “containment” was an American diplomat called George F. Kennan, who had studied Russia’s language and history as a young man. In February 1946, Kennan, then deputy head of mission in Moscow, had sent a long telegram to Washington urging his bosses to ditch any idealistic assumptions about reaching a modus vivendi with Stalin.

“At the bottom of the Kremlin’s neurotic view of world affairs”, he argued, was a “traditional and instinctive Russian sense of insecurity”. And though Kennan took Stalin’s Marxism seriously, he thought it was mixed up with something else, something older, perhaps even darker. For in some ways, he wrote, Marxism was simply the “justification for the Soviet Union’s instinctive fear of the outside world, for the dictatorship without which they did not know how to rule, for cruelties they did not dare not to inflict, for sacrifice they felt bound to demand”.

What Kennan also recognised, though, was that for all Stalin’s purges and persecutions, even his imposition of puppet governments in the brutalised capitals of central and eastern Europe, the Americans could not just fight him. Even with their nuclear monopoly, they would probably incur hundreds of thousands of casualties as they tuned their guns on the Red Army. Europe would be utterly devastated; the total death toll would probably run into millions. There was right, and there was wrong; but doing the right thing was complicated.

So as Kennan argued in a subsequent article, the West really only had two options. They could sit back and let Stalin get away with it, playing the part of appeasers once again, and allowing him to erode democratic freedoms in one European country after another. Or they could draw a line and say: “This far, and no further”, and do all in their power to undermine those regimes that flew the red flag. Their strategy, wrote Kennan, “must be a long-term, patient but firm and vigilant containment of Russian expansive tendencies”. They would corral the Eastern monster and defend Western freedom by “a policy of firm containment, designed to confront the Russians with unalterable counter-force at every point where they show signs of encroaching upon the interests of a peaceful and stable world”.

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As Kennan and Truman both knew, containment would take time. Not months, not years, but decades. There was nothing very romantic about it, nothing swashbuckling. It condemned millions of people to continue living under totalitarian rule. If you were 17 in 1947, and living in Poland, Hungary, Czechoslovakia or East Germany, you would be very close to retirement when the Berlin Wall came down. You would have spent almost your entire adult working life under a system you probably despised, with Russian troops occupying your country. All that potential wasted; all those chances for travel and self-expression denied you; all those lies, all those betrayals. But you would still be alive — and with luck, you would see your grandchildren grow up in freedom. Those were the upsides.

So let’s turn to the present. With the headlines full of the atrocity at the Mariupol maternity hospital, the slaughter of Ukrainian civilians and the looming siege of Kyiv, as well as Volodymyr Zelenskyy’s rousing Churchillian rhetoric, it’s easy to dismiss containment as a kind of appeasement, an acceptance of defeat. Most of us would love to see Russia defeated, its troops streaming back home to launch a revolution and Vladimir Putin on trial in the Hague — just as most decent people in the late 1940s and early 1950s dreamed of seeing Stalin toppled and Communism overthrown from Trieste to the Baltic.

But in truth this feels depressingly unlikely. For the time being, the Putin regime seems entrenched. And of course Putin has something Stalin didn’t in the spring of 1947 — nuclear weapons. That’s why most Western politicians have ruled out a no-fly zone over western Ukraine. It’s entirely understandable that people think we should “do something”. But there’s no point in doing something if the firestorm kills the very people you were hoping to save.

Containment was precisely the kind of policy you would expect from a man who had run a gentlemen’s outfitters in Kansas City. But you can tell that story in two different ways. Yes, it was unglamorous, gradualist, boringly undramatic. Yes, there was nothing obviously heroic about it.

Yet at the same time it reflected a very Middle American confidence in the Western way of life. Like his British counterpart, Clement Attlee, Truman was a modest man, the incarnation of patriotic ordinariness. He believed, without the slightest shadow of doubt, that one day democratic capitalism would beat Communist repression. But he also knew it would take years of effort, and he had no intention of blowing up the world in the meantime.

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There’s part of me, I admit, that feels wretched in urging a policy of Cold War containment on the leaders of the Western world. Against the background of so much Ukrainian suffering, the thought of Vladimir Putin’s regime enduring for years — and not just surviving but glorying in slaughter — seems almost intolerable. But what are the alternatives? Appeasement, as recommended by certain so-called realist professors of international relations, strikes me as not merely morally contemptible but stupidly self-defeating. As for NATO intervention, how many Ukrainians would die in even the most limited nuclear exchange? Millions? Tens of millions?

Truman didn’t live to see the success of his policy. In very basic terms, though, containment underpinned the Western world for the next 40 years. The Cold War was a hard slog, involving a lot of false steps as well as some dreadful mistakes. But it worked. That was the important thing. I sometimes read that we should never return to the Cold War. But why not? It was the right thing to do, and the right side won.

And remember: Soviet Communism was a much more formidable adversary than Putinism. The latter offers nothing but a nihilistic celebration of warmongering nationalism, but Communism held out the promise of a better world, illusory as that was. Containment beat it, all the same.

I think it will beat Putin, too, given time. It may take years of unrelenting political, economic and cultural pressure, but we should have no doubt about the outcome. The little man from Missouri has already beaten Lenin and Stalin. Even in death, he can wipe the floor with Vladimir Putin.