Roger Moorhouse is historian of the Second World War. His latest book, First to Fight: The Polish War 1939 is published by Bodley Head.

Edgar Vincent is one of those politicians who has slipped from public consciousness almost completely. Once a prominent businessman, an MP and British Ambassador to Germany, he was elevated to the peerage in 1914 as 1st Viscount D’Abernon, a title that died with him when he passed away in 1941.

In one regard, however, Vincent did leave a legacy. His memoir of one of the salient periods of his career — his time as a British Envoy to Warsaw in 1920 — made the grand claim that the fight for the Polish capital that summer was one of the most important battles in world history; alongside Marathon, Blenheim and Hastings. Yet, the Battle of Warsaw — like much of Polish history — is almost unknown to English-speaking audiences.

The year 1920 was one of chaotic flux across much of Europe. The baleful effects of the industrialised slaughter of the First World War were still being felt, and in central and eastern Europe states newly emerged from the collapse of the German, Austrian and Russian empires struggled to unify and assert themselves. As Winston Churchill pithily summarised: “The war of giants has ended, the wars of the pygmies begin.”

Poland provided perhaps the most pressing example. Reappearing on the map in 1918 after a 123-year absence, during which time it had been partitioned by its larger neighbours, Poland filled something of a central European void, in the process fighting a number of squabbles and conflicts in attempting to define its frontiers.

The war that saved Europe from Communism By Roger Moorhouse

The most serious of these was the Polish-Soviet War, which had begun in the early spring of 1919, when Polish forces had engaged those of Lenin’s Red Army in what is now Belarus. The conflict that followed was no pygmy sideshow — it would last for more than 18 months, range over hundreds of miles and cost the lives of more than 100,000 men.

So it was that Polish and Soviet forces engaged that spring. What followed was a curious conflict, far removed from the static, industrialised warfare that had recently drawn to a close in the west of Europe. Here, across the vast expanses of what is now Belarus and Ukraine, where roads and infrastructure were sparse, more traditional — and more mobile — methods of war prevailed. Armoured trains played a role, but cavalry was king. Poland’s Uhlans and the Bolshevik Konarmia — the Red Cavalry, which would become synonymous with a proto-Blitzkrieg of brutal ideologically-charged warfare — took centre stage in campaigns that ebbed and flowed across the landscape, ranging from the Ukrainian capital, Kiev, to the very gates of Warsaw.

By the summer of 1920, however, the war appeared to be nearing its end. Polish forces were in headlong retreat, driven westward by the numerical superiority of their enemy. They had already lost the cities of Lwów, Brest-Litowsk and Zamość, and were now in danger of losing the capital itself. Poland’s new-found independence, it seemed, was about to be snuffed out after less than two years.

But, in the middle of August, a desperate Polish counterattack to the east of Warsaw drove northward into the overextended Soviet flank, finally halting the Red Army’s advance in a ten-day engagement, at the cost of around 20,000 lives. Known to Poles as “The Miracle on the Vistula”, the battle not only relieved the capital, it routed Soviet forces, scattering them north into East Prussia and Lithuania. With that, the Soviet front collapsed, and the Kremlin finally sued for peace.

The war that saved Europe from Communism By Daniel Kalder

The consequences of the Miracle were far reaching, with Poland securing its independence for a generation, its place on the map of Europe not challenged again until 1939.

In addition, the Soviet defeat arguably poisoned Kremlin attitudes towards the Poles. Relations between the two Slavic nations were never rosy — the long years of Russian partition and oppression had seen to that — but the Bolsheviks saw themselves as a new dawn, with a seductively universal ideology. Yet, outside Warsaw, they found that their message of socialist fraternity was decisively rejected; their vanguard of revolution — the Red Army — roundly defeated. As Stalin would later complain, bringing communism to Poland was “like putting a saddle on a cow”.

This rejection would have profound consequences. Soviet anti-Polish sentiment resulted in the execution by the NKVD secret police of over 100,000 Poles living within the Soviet Union in 1937-8, in a systematic attempt to eradicate them as an ethnic minority. More ominously still, a shared desire to destroy Poland was instrumental in bringing Hitler and Stalin together to agree the Nazi-Soviet Pact in August 1939.

And, following their invasion of Poland three weeks later, Soviet forces were predictably brutal, targeting the Polish officer class and educated elites with persecution, deportation and execution. One might conclude that the road to the death pits of Katyń forest — where many of the 22,000 Polish officers executed by the Soviets in 1940 were killed — began two decades earlier with the Soviet defeat outside Warsaw.

Stalin also had a personal reason to look back on 1920 in anger. At that time, he was commander of the south-western front, around Lwów, and was widely criticised as culpable for the failure to adequately reinforce the Warsaw front. Rebuked by Lenin, the Politburo and the Supreme Command, he was humiliated, even scapegoated, and simmered with anger thereafter. Coincidentally or not, his most vociferous critics – Trotsky and Tukhachevsky among them – would all later feel the hot lead (or cold ice-pick steel) of his ire.

And yet, significant though these aspects are, they were unknown to D’Abernon as he wrote his memoir in 1930. So why then, did he rate this still little-known battle as one of the most important military engagements in human history? The answer lies in the realm of grand strategy.

For Moscow, spreading communism westward in 1920 was not only desirable, it was an ideological imperative. In Marxist ideological terms, the Russian revolution made little sense. After all, Marxism foretold that communism was supposed to be the inevitable, scientifically determined, result of the collapse of capitalism. And yet, the first country to become communist had scarcely entered its capitalist phase; its industrial proletariat class was miniscule and insignificant.

The vital imperative, therefore, was to spread communism westward to more advanced, industrialised countries — most importantly Germany — not only to secure the revolution at home, but to make the entire edifice of communist revolution make ideological sense.

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And Germany in 1920 was in a state of near-collapse; its economy in ruins, its population exhausted, angry and disillusioned, its political life fraught with revolutionary tensions on both Right and Left. If there was ever a time for the Red Army to ride in to spur the German communists and other malcontents to victory, it was now. It was no surprise therefore that Tukhachevsky’s order of the day to his troops implored them to “Go West! Over the corpse of White Poland lies the road to worldwide conflagration!”

Yet the Poles would prove to be very un-corpse-like. For one thing, the supposedly “universal” appeal of communism proved pretty unappealing to them, prefaced as it had been by a brutal military campaign and imported alongside an army of secret policemen, militiamen and “requisitioning agents”. Moreover, for many Poles, anything imported from the east was automatically tainted by association with Russia, Poland’s historic oppressor and occupier.

Consequently, the Poles bitterly resisted the horsemen of the revolution, handing the Soviets a crushing defeat at the very moment that victory appeared to be within their grasp. In so doing, they checked the Kremlin’s ambitions, dented its apparent ideological sheen, and crucially saved a west that — in that moment — was on its knees.

It was this that D’Abernon was referring to in raising Warsaw to the Pantheon of history’s most significant battles. In his book, he opined that, had the Poles “failed to arrest the triumphant advance of the Soviet Army at the Battle of Warsaw, not only would Christianity have experienced a dangerous reverse, but the very existence of western civilisation would have been imperilled.”

Just as the Battle of Tours “saved our ancestors from the Yoke of the Koran”, he concluded, so the Battle of Warsaw saved Western Europe from “a far more subversive danger – the fanatical tyranny of the Soviet.” D’Abernon’s language may not have been that of the modern diplomat or politician, but his fundamental historical judgement was sound. It is hard not to conclude that in this at least he was right.

Warsaw in 1920 represented that rare thing in history: a moment of genuine existential peril, akin to the Battle of Britain or Waterloo. We in the English-speaking world would do well to remember it.