The Soviet writer Ilya Ehrenburg once wrote that war comes very early to the theatre. He stands around for a long time in the wings, waiting for his performance to begin.

Nearly a century later, it’s generally assumed that the second world war was inevitable. Was it? In contrast to all the intriguing arguments about the origins of the first “Great War”, most people accept that this war was long foreseen and that its cause can be reduced to a single word: Hitler. That consensus is too comfortable not to be challenged.

The historian Eric Hobsbawm wrote that “we who lived through those times knew that there would be a war, even as we sketched out unconvincing scenarios for avoiding it”. Many have blamed the Versailles peace treaties of 1919 for designing a Europe of unsatisfied nationalisms to which Hitler merely put the torch. Will Dyson’s 1919 drawing “Peace and Future Cannon Fodder” is the most dreadfully prophetic of all political cartoons. The Big Four world statesmen are emerging from Versailles, past a naked toddler labelled “1940 Class”, and French prime minister Georges Clémenceau is saying: “Curious! I seem to hear a child weeping.”

Facebook Twitter Pinterest Will Dyson’s 1920 cartoon Peace and Future Cannon Fodder. Photograph: Chronicle/Alamy

But the Versailles settlement might not have ended in catastrophe, even though it made some sort of resentful German revival inevitable. Fascism was the trouble – fascism in a time when the liberal democracies were too weak to resist it or to defend the Versailles status quo. France and Britain were never, until the very end, quite able to grasp that the dictators were not rational, that deterrents did not deter them and that a diplomacy which offered concessions seemed to them an admission of weakness.

AJP Taylor, a historian who liked upsetting received ideas, wrote that Hitler never had a coherent plan of conquest but simply grabbed opportunities. Neville Chamberlain, who became British prime minister in 1937, did have a plan for dealing with Hitler, “deterrence with negotiation from strength”. But how do you negotiate with somebody completely unreliable and capricious?

Until 1939, Chamberlain resisted the idea of an anti-German alliance which would include the Soviet Union. He didn’t want Hitler to feel “surrounded”. (And much of the Conservative party, while disliking both tyrannies, instinctively preferred the Nazis to the Bolsheviks.) It wouldn’t have worked, anyway. Even if Stalin had honoured an agreement, the Polish government would never have joined a military pact with the traditional Russian enemy. And when Chamberlain changed his mind, it was too late. In August 1939, Nazi Germany and the USSR signed their infamous non-aggression pact which secretly agreed on the partition of Poland and the abolition of the Baltic states.

The year before, a complacent Chamberlain had “saved the peace” at Munich, by forcing the Czechoslovak government to surrender the Sudeten territory to Germany. “Hitler has missed the bus,” he told his cabinet. But in March 1939 Hitler tore up the agreement and invaded the Czech lands, reducing them to a German “protectorate”. Chamberlain was shattered. But ever since Munich, British opinion had been swinging round from “appeasement” to a sombre recognition that the country must now prepare for war.

The war broke out because, unexpectedly, Britain did something reckless. Germany was escalating demands for Polish territory and the “free city” of Danzig. On 30 March 1939, Britain and a reluctant France issued a guarantee of Polish independence. Soon afterwards, the guarantee was extended to Romania and Greece. Most of Europe knew this would not stop Hitler and that war was imminent. Strangely, Chamberlain didn’t. He thought the guarantee would put Hitler off, and horrified the House of Commons by suggesting that the promise only protected Poland’s independence – not its territorial integrity.

The invasion of Poland began on 1 September 1939. Britain and France declared war two days later. Hitler had never believed that the British would fight. He had always intended to have a war – Poland, France, Russia eventually – but not this one. In contrast to the patriotic fervour of 1914, the German people went into this conflict full of gloom and foreboding, a mood which only cleared after the dazzling victory over France in 1940. The British did not cheer either. A few years earlier, prime minister Stanley Baldwin had told them that “the bomber will always get through… when the next war comes and European civilisation is wiped out…”

So began the 21 months of European war – not yet world war. The Poles fought bravely but were crushed by Nazi and Soviet armies advancing from west and east. The USSR invaded Finland. Britain and France did nothing militarily to fulfil their guarantees to Poland, and spent a static winter confronting the Germans across the French frontier. Could this war – should it – have been avoided?

Hitler would almost certainly have attacked France sooner or later. But Britain? To this day, a few historians think that the Polish guarantee was a fateful mistake. In this view, Chamberlain’s previous policies offered the only hope of avoiding war, saving the British empire and perhaps preventing the postwar world’s domination by only two superpowers.

In April 1940, Germany invaded Denmark and Norway. In May, Hitler launched the tremendous offensive which overran Holland, Belgium and France, and threw the small British army out of Europe at Dunkirk. The Battle of Britain denied Hitler the air superiority he needed to cross the Channel, but Benito Mussolini now thought it safe to bring Italy into the war and occupy a sliver of France.

Facebook Twitter Pinterest German troops march into Prague during the invasion of Czechoslovakia in 1939. Photograph: Three Lions/Getty Images

Hitler had in fact won the war by the late summer of 1940. Britain, he thought, could now be bracketed out. Winston Churchill made brave speeches, but Britain was isolated and some members of Churchill’s cabinet were quietly angling for a “commonsense” deal with Germany to end hostilities. Hitler had conquered seven countries with a population of more than 100 million, from the Arctic to the Mediterranean, from the Atlantic almost to the Black Sea. The rest of “neutral” Europe cowered. The Soviet Union and the US showed no immediate sign of wishing to join the conflict. Why, then, was this not the end of the story?

***

It was time for my father to leave for work at the torpedo factory. But he suddenly jumped up from the breakfast table and went to the window to stare at the morning sky. I can still hear the exultation in his voice. “Now I know we are going to win the war!”

The wireless had just told us that Nazi Germany had invaded the Soviet Union. It was 22 June 1941. It was the day when an Anglo-German war began to turn into a world war. It was the day when Hitler set in train his own failure and death and the destruction of his country. And it was the day that designed the postwar world.

In the cold war years, the mighty Sebastian Haffner of the Observer used to say: “We are living in Hitler’s Europe.” He meant that on that June morning, Hitler had made three things inevitable. The first was his own defeat; in the long run, no invader could overcome the colossal resources of Russia and the courage of its peoples. The second was that Germany would not only be devastated but would be broken up into satellite states shaped by the victors. The third was that Russian power would surge forward right into the centre of Europe – something western statesmen had struggled to prevent for two centuries. There the Soviet armies would meet Anglo-American armies entering Germany from the west, a confrontation which would lead to the permanent division of our continent into two hostile camps – the cold war. We were to live in “Hitler’s Europe” until 1989 (with the collapse of the Berlin Wall).

Facebook Twitter Pinterest An ambulance driver of the British Women’s Auxiliary Army in 1940. Photograph: Hulton Archive/Getty

By the summer of 1941, in any case, the war was starting to spread beyond Europe. China’s long war against Japanese imperialism was still a separate affair, but north Africa had become a battlefield as the Italians, and then the German Afrika-Korps attempted to drive the British out of Egypt. The British pushed Italy out of Abyssinia and Eritrea, and suppressed a pro-German rising in Iraq. And under the Royal Navy’s protection, troops and equipment from India and colonial Africa were pouring into north Africa and Britain itself.

***

Late in 1941, two almost insane decisions completed the transformation into a true world war. On 7 December Japanese aircraft attacked the American fleet at Pearl Harbor in Hawaii. In doing so, they challenged the Pacific’s superpower to battle just as they were engaged in a gigantic offensive to conquer the French, British and Dutch empires in south-east Asia – a gamble that succeeded at first but ultimately turned out to be far beyond Japan’s resources.

A few days later, Hitler inexplicably declared war on the US. There was no sober reason for it, beyond showing solidarity with Japan. It’s hard to remember now how little Europeans (and Americans) knew about foreign countries in those days. Hitler genuinely believed that the US was a nation of pampered cowards, “half Judaized, half negrified”, unable to produce real soldiers.

President Roosevelt had been arming and supplying Britain for more than a year. But now America joined Britain and the Soviet Union as a full member of the military alliance dedicated to the defeat and “unconditional surrender” of Germany and Japan, as well as Italy. Troops, aircraft and supplies flowed into Britain; American equipment reached Russia on perilous Arctic convoys. Almost at once, the Americans began to urge Churchill to launch an invasion of Nazi-held France, to relieve the pressure on the Soviet Union. Stalin joined the chorus for a second front in 1942.

Churchill refused. Years more preparation were needed if a cross-Channel invasion were not to fail. Meanwhile, 1942 was a grim time for Britain as Japan collapsed the British empire in south-east Asia, conquering Malaya and Singapore and marching through Burma towards India. But it was on the eastern front, in the Soviet Union, that the outcome of the war was decided. Hitler had invaded Yugoslavia and then Greece, critically reducing the strength he needed in Russia, and on 8 December 1941 – the day after Pearl Harbor – the Nazi advance was finally halted in the snow a few miles before Moscow.

Facebook Twitter Pinterest British, Australian, and Indian troops surrender to the Japanese as Singapore falls in 1942. Photograph: Popperfoto/Getty Images

But it was not until early 1943 that the tide of this colossal struggle began to turn, as the German 6th Army, cut off at Stalingrad, was forced to surrender after losing 140,000 dead. The decisive battle began in July at Kursk, the biggest tank battle in history, as the Red Army (well warned by spies) attacked the flanks of a huge Nazi thrust. Two million men and nearly 6,000 tanks took part. After Kursk, the Soviets began an inexorable advance which would bring them, two years later, to Berlin.

Elsewhere, the anti-Axis coalition was at last winning campaigns and liberating territory. The Americans landed in Algeria and, with the British driving victoriously across Libya, threw the Germans out of north Africa. Soon the Allies had taken Sicily and – as Italy dropped out of the war – American, British, Polish, French and New Zealand troops were fighting their way up the Italian peninsula.

Stalin dominated the Teheran conference of the “big three”, held at the end of 1943. The Red Army was carrying the main burden of the war in Europe. Churchill had not yet launched the promised cross-Channel invasion, and the strength of the US war economy was only beginning to show as Japanese and American air and naval power clashed in the Pacific. President Roosevelt did not press Stalin about his plans for “liberated” Europe. Instead, he welcomed Soviet support for a “united nations organisation” after the war, and Stalin’s promise to attack Japan.

***

In June 1944, the Allies finally stormed the Normandy beaches. After months of fierce fighting, the Germans retreated and by the end of the year France, Belgium and most of Holland had been liberated. The invasion was coordinated with another huge Soviet offensive, which broke through and drove on to the outskirts of Warsaw. The city rose to free itself before it fell under Soviet control, but the Red Army halted and allowed the Germans to suppress the rising and massacre the population.

By the summer of 1944, it was obvious that Germany had lost the war which it had won in 1940. But it dragged on for another nine months. Armies fought their way into the Reich from east and west; German cities crumpled under the obliterating firestorms of Allied bombing; Germany’s children died clutching anti-tank grenades while their mothers and sisters were raped by the invaders. Why?

There were four main reasons why the Reich fought on. The first was the Allies’ insistence on “unconditional surrender” – no negotiated peace. The second was the incredible resilience of German soldiers, who never seemed to lose their power of instant counterattack. The third was the hypnotic grip of Adolf Hitler’s personal cult, decaying into a belief that loyalty to somebody, to anybody or anything, was the last lifebelt in an ocean of meaningless horror.

Facebook Twitter Pinterest The young fighters of the Hitler Youth were caught in Hitler’s hypnotic grip. Photograph: ullstein bild Dtl./Getty

The fourth reason was that many Germans, not only leading Nazis, knew what had been done in their name. From the Russians, at least, they expected no mercy. But, strangely, efforts to conceal evidence of the greatest crime of all, the murder of six million Jews, were late and erratic. In that summer of 1944, the Auschwitz gas chambers were still killing 10,000 Hungarian Jews a day (the last death train reached Auschwitz at the end of October).

***

On 29 April 1945, as Russian troops closed in on his Berlin bunker, Hitler killed himself. On 7 May, after a messy series of local surrenders, Germany finally stopped fighting. Two historic conferences between the victorious Allies, Yalta that February and Potsdam in July, confirmed the future outlines of “Hitler’s Europe”, a cold war continent divided between two hostile military pacts, with a few nervous neutrals on the fringes.

At Yalta, Roosevelt and Churchill accepted that the half of Europe already “liberated” by Soviet forces would remain a Soviet zone of influence. Its countries became Moscow’s puppets for the next 44 years, suffering decades of police terror, censorship and privation. The fate of Poland, which had suffered atrociously under Nazi occupation while staying loyal to the Allies from the first day of the war to the last, was especially agonising. To this day, Poles consider that the west sold them out at Yalta. But by then, only a third world war might have pushed Soviet power back to its own frontiers.

The second world war had only one unqualified winner: the US. Defeating Japan, expected to take several more years and cost a million casualties, was achieved on two days that August, as atomic bombs incinerated Hiroshima and Nagasaki together with their inhabitants. America emerged as by far the greatest industrial power on earth, supplying almost insatiable demand from its own internal market and from the reconstruction of a ruined western Europe – given hard-currency purchasing power through the Marshall Plan. There followed the “American half-century”, in which the US’s hegemony – economic, cultural and military – controlled most of the non-communist world.

The first world war had destroyed the old land empires of Eurasia by military defeat and revolution. The second world war led to the slow foundering of Europe’s colonial empires – British, French, Dutch, Belgian and Portuguese. Military experience, spreading education, the ideals of the Russian Revolution, even the sudden leap in earnings caused by wartime demand for African and Asian raw materials, all encouraged colonised peoples to demand independence. It was won sometimes by negotiation, sometimes by bloody and prolonged “liberation struggles”.

The world atlas changed colour. So did the streets of western Europe. Old imperial states, traditionally identified as white and Christian, now began to receive a massive inflow of immigrants, at first from north Africa and the Caribbean, later broadening to draw in settlers from south Asia and tropical Africa.

These migrations followed the colossal population movements within Europe as the war ended. Millions took to the roads home as the Reich’s forced labourers escaped and the gates of the concentration camps fell open. Ethnic cleansing on an unimaginable scale drove some 12 million Germans from their homes in eastern and central Europe. Polish families uprooted from their villages in Belarus or Ukraine moved into renamed German cities whose inhabitants in turn had been expelled. Far to the east, Stalin deported Chechens, Tatars and Greeks to starve in central Asian deserts.

Facebook Twitter Pinterest Bergen-Belsen concentration camp in May 1945. Photograph: George Rodger/Life/Getty

In those six years of war, the world had shrunk. Continents got to know one another. Rural English girls goggled at black American soldiers, then adored their courtesy and their dance steps. In Nazi Berlin, teenagers listened to Dizzy Gillespie on American Forces Network, growing clearer as the tanks drew nearer. At my school, we lay in the grass – the turf trembling in the thunder from five miles above us, as hundreds of silvery Liberators passed in formation to bomb France – and we said: “Maybe everybody will fly everywhere after the war. Maybe we’ll go to Alaska and meet Eskimos, and then Africa and meet real Zulus.”

Europe seemed a dark place, where the Germans crouched and horrible stuff happened. But one day the headmaster gathered us to hear a poem written “over there” and somehow smuggled across the Channel by the Resistance. It was by Paul Éluard: “I was born to know you, / To utter your name / Liberté.”

Resistance, its memory and myth, restored to Europeans a scrap of dignity under Nazi occupation and afterwards. Except in Poland and above all in Yugoslavia, its military impact was minor. But liberté came to mean more than chasing out the Germans. It meant change. Europe experienced a “resistance moment” from about 1943 to the start of the cold war in 1947, in which men and women emerged from clandestinity to demand and plan radical national renewal. Their prewar governments, they believed, had surrendered to fascism because they were corrupt, grossly unequal, lacking moral legitimacy. Now socialist and communist ex-partisans, many of them survivors of Gestapo torture, dominated many of the first post-liberation governments. But it was not long before growing cold war paranoia, Stalinist or anti-communist, broke their alliance apart.

Resisters were usually a tiny minority. Most people in Nazi-occupied Europe had spent hungry, humiliating years keeping their heads down. Only afterwards did they recover self-respect by identifying with the patriotic sacrifice of the few. It took a generation before France could admit that – for example – French officials had arranged the transport of 4,500 Jewish children to be gassed and burned in the Nazi death camps.

The ruins left by the war were moral as well as physical. Our Europe is built on them. The dream of a united Europe started as a plan to rebuild the integrity and authority of its disgraced nation states, something which those states were still too weak to manage by themselves. The vision of a supranational union without internal frontiers, making future wars unthinkable, was secondary. Later, Charles de Gaulle was to talk of a Europe des patries, rather than a United States of Europe. He is still right.

The “resistance moment” led into the Trente Glorieuses – the 30 years in which the peoples of western Europe mended their wreckage and became more prosperous, more secure, more equal and better educated than ever before – or since. Britain, too, had used the war years to plan the great postwar settlement which seemed – for a time – to be consigning poverty, gross wealth and health differences, inflation and “bankers’ economics” to history. People looked back at the war and the 1930s, and said: “Never again!”

The ruins left by the war were moral as well as physical. Our Europe is built on them

And yet Britain was turning in on itself as the war ended. “We stood alone against Hitler.” But Britain was actually more isolated in the postwar decades than in 1940. Back then – for all its marvellous defiance after Dunkirk – Britain was supported by the armed forces of the Commonwealth and the resources of the empire, to say nothing of American aid.

Myths about wartime soon took hold. Hadn’t Britain triumphed by just being itself – by being the comically amateurish, strangulated and yet quietly heroic England of the conservative vision? Films made in wartime starred soldier-characters who often didn’t talk posh. But in the war movies of the 1950s and 1960s, the heroes were usually officers with public school accents.

Perhaps, too, things seen or experienced in that war left the British with a special trauma, a revulsion against the outside world. When British troops entered the vast concentration camp at Bergen-Belsen, a decision was taken to bring as many soldiers as possible – young officers especially – to see it. I came to know quite a few of them later.

All were deeply damaged. They had known about Nazi brutality, of course, but this… it was beyond just “the Germans”. They had no idea that human beings of any description were capable of this. French, Polish, Dutch witnesses did have at least an idea. But these officers were damaged not only in their English innocence but in their own sense of humanity. If Europe was a place where such things were imaginable, how intimate with Europe could one become?

***

Sometimes the cruelty of war shows more clearly in small, quiet scenes than in battles and bombings.

When I think of the second world war, I see the platform of an English railway station, in the bitter cold of a wartime night. A train is waiting, a wisp of white steam flickering in the lamplight. My mother and I have brought P and her fiance to the station. He is returning to his submarine. The odds on him and his crew surviving are not good.

We sit on a bench outside the ticket office, while P – smiling hard – walks with her man to the end of the platform. Nobody else is about. We can just see them as he leans out of the window of the compartment, their heads close together. Then the engine whistles, the train begins to move. P stands still, as the carriages and finally the red tail-light on the guard’s van slowly pass her and vanish into the night.

Facebook Twitter Pinterest A sailor kisses his sweetheart goodbye at a railway station. Photograph: George W Hales/Getty

Alone, she starts back towards us, very upright and brisk-stepping. My mother, a naval wife who knows about farewells, opens her bag and takes out two large, clean white handkerchiefs. She stands up.

P has come quite close to us when I see her knees begin to buckle. My mother moves swiftly to catch her as she falls and guide her to the bench.

I walk away for a while, so I don’t hear or see. I’m a wartime child, so I too know this routine. Wartime, peacetime, like winter and summer, the natural alternation. It’s a cruel moment, and I have learned that war is cruel. But nobody has taught me yet that war doesn’t have to happen.

Brave new world: Andrew Rawnsley on the search for peace and prosperity