What was history's biggest blunder? 9 experts have their say

Our team of historians, broadcasters and authors reveal the monumental mistakes that changed the course of history

An illustration of a statue resembling Rodin’s “The Thinker,” seated with its chin on one hand. A pigeon perches on the statue’s head and has left a white splatter, adding a humorous touch. The statue sits on a pedestal marked with the Roman numerals “MMXXVI” against a plain light‑blue background.

Published: June 24, 2026 at 3:30 PM

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Xerxes's overconfidence

How Greek cunning lured Persia’s vast naval fleet to destruction

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The Persian king Xerxes came to Greece in 480 BC with an enormous army and navy, determined to destroy Greece once and for all. With Xerxes’s fleet bearing down on the much smaller Greek one, the Persians knew there was no way the Greeks could beat them in open water – their numbers were too great.

An ancient stone relief showing a bearded figure in profile, carved with tightly curled hair and a tall headdress. The figure holds a long staff in one hand and a flower‑like object in the other. The carving is detailed and symmetrical, set against a flat stone background.

Xerxes, depicted above in a relief, was confident that his mighty military would easily overpower Greece, but he was outmanoeuvred | Credit: Getty Images

The Greeks knew this, too, and had a plan. Led by the Athenian Themistocles, the Greek fleet tricked the Persians into sailing into the narrow straits of Salamis, an island just off the coast of Attica (the territory of the city of Athens). There, in the choppy waters with difficult currents only known to locals, the vastly bigger Persian numbers counted for naught, and the Greek fleet was able to decimate their Persian foes. The Persian king’s invasion plans were in tatters, and he left Greece soon afterwards with his tail between his legs.

If the Persian king had not fallen for the Greek trick at the battle of Salamis, it is likely that Greece would have come under Persian control in 480 BC and the whole of ancient history – and indeed modern history – would have looked very different.

Michael Scott, professor of classics and ancient history at the University of Warwick

Appeasing Hitler

By trying to avoid a Second World War, the Allies guaranteed one

If the greatest tragedy in world history was the Second World War, then our greatest blunder was the failure to stop it. There were many opportunities to do so, especially in Europe.

Hitler’s aggressiveness first became obvious in 1935 when he revealed that he had been rapidly rebuilding Germany’s air force and army. This was a clear breach of the peace agreement signed after the First World War. Perhaps if Britain and France had stood up to Hitler then, they might have discouraged him from trying anything so obviously hostile again.

A black‑and‑white photograph of soldiers in steel helmets marching in formation down a city street. Buildings along the route are decorated with large Nazi flags, and civilians on the pavements and balconies raise their arms in salute as the troops pass.

German troops march into the Rhineland, 1936. This was just one of many occasions when the Allies turned a blind eye to Hitler’s hostile ambitions | Credit: Alamy

The following year, Hitler marched his troops into the Rhineland – the region of Germany near the border with France that was supposed to remain demilitarised. In reaction, Britain and France did nothing. In 1938, Germany forcibly annexed Austria. Again, there was no response. When Hitler began bullying Czechoslovakia a few months later, he was not punished. In fact, quite the opposite happened: attempting to placate him, Britain and France gifted him Czechoslovakia’s Sudetenland. It was almost as though they were rewarding him for his aggressiveness.

There were good, strong reasons for this policy of ‘appeasement’. Memories of the First World War were still strong in the 1930s, and British and French politicians were willing to do anything to avoid a repeat of that carnage.

But they were forgetting the famous advice that military strategists have repeated ever since the time of ancient Rome: ‘If you want peace, prepare for war.’ The failure of Britain and France to prepare for war led to the greatest conflict in history and, ultimately, to the deaths of at least 35 million people.

Keith Lowe, author of The Fear and the Freedom: How the Second World War Changed Us (Viking, 2017)

Harald's fatal miscalculation

The Norse king believed the hype – and brought the Viking Age crashing down

Nicknamed the ‘Thunderbolt of the North’ by chronicler Adam of Bremen, King Harald Hardrada of Norway was a legend in his own lifetime, a hero of sagas and poems. He was a successor to King Cnut, who had created a North Sea empire that included England, Norway and Denmark, and Harald saw England as his birthright. In September 1066, he crossed the North Sea with a fleet of some 300 ships and thousands of warriors. What could go wrong?

The Norse fleet landed on the north-east coast of England and joined forces with their ally on the inside: Tostig Godwinson, disgruntled brother of King Harold of England. On the outskirts of York, they defeated Morcar, Earl of Northumbria, and his brother Eadwine, Earl of Mercia.

A medieval manuscript illustration showing an armoured battle scene. Knights in chainmail and helmets clash with swords and shields, some on horseback. Their shields display different heraldic designs. At the centre, a crowned figure in a red surcoat stands out amid the chaotic fighting. The scene is framed by a simple red‑and‑white border.

The Battle of Stamford Bridge, illustrated here in the 13th-century Life of St Edward the Confessor, was a masterclass in bad planning | Credit: Getty Images

Meanwhile, despite rumours of an invasion on the south coast, England’s King Harold Godwinson raced north with his army in four days, covering almost 200 miles. Waiting at Stamford Bridge for the delivery of hostages, Harald Hardrada’s troops were
unprepared for battle. It was said that many of them had left their armour on their ships. When Harold Godwinson’s army appeared – fast, disciplined and furious – it was too late. The Vikings fought heroically, but courage can’t fix bad planning. Hardrada was killed and his army was shattered. Of the roughly 300 ships that brought them to England, only about two dozen were needed to take the survivors home.

The battle of Stamford Bridge wasn’t just a defeat. It was the Viking Age tripping over its own legacy. Ambition outran strategy and – symbolically at least – ended an era.

Eleanor Barraclough, historian, broadcaster and author of Embers of the Hands: Hidden Histories of the Viking Age (Profile, 2024)

Underestimating the power of nature

When a simple fix unleashed one of the world’s most invasive species

In the US South, legend says it can grow multiple inches a night. It looks like English ivy’s jacked-up cousin, and researchers count it among the 100 most invasive species in the world. Kudzu (Pueraria montana), a woody green vine originating in Asia, was introduced to Americans at the 1876 Centennial Exposition in Philadelphia. But it wasn’t until the Dust Bowl of the 1930s, when agricultural officials used it to stop erosion and renew over-farmed land, that the vine really took off. Unfortunately, it turns out kudzu hides rather than stems erosion. According to researchers for the US Department of Agriculture, it wreaks havoc on native ecosystems by “gobbling up” acreage and “smothering” other plants.

A dense green landscape where thick vines blanket the ground, trees, and hillsides, creating rolling mounds of vegetation. A deep valley cuts through the scene, and dark grey clouds hang overhead, suggesting an approaching storm.

Kudzu was introduced to prevent erosion; instead, it smothered landscapes across the US | Credit: Getty Images

Kudzu now thrives on all continents except Antarctica. It blankets American landscapes, enshrouding light poles and engulfing small outbuildings. Foresters have tried eradicating it by feeding it to goats, and companies have tried to make it productive by feeding it to people as flour or blossom jelly.

The history of technology and intervention often involves “people trying to solve problems created by people trying to solve problems”, notes science writer Elizabeth Kolbert. With kudzu, as with so much, the great blunder lay in thinking that the next new thing would allow us to continue the same old practices, in emphasising innovation over radical change.

Adriane Lentz-Smith, associate professor of history at Duke University

Columbus's 1492 expedition

A daring maritime gamble that unleashed centuries of devastation

In 1492, Christopher Columbus was aiming for a westward sea passage to far-eastern Asia. When he sighted land, he was convinced he’d made it to the Indies. He hadn’t, but it was nevertheless an extraordinarily impressive expedition in terms of navigation, maritime skill and sheer determination.

An old engraved scene showing European explorers landing on a shore. Several men in 16th‑century clothing stand on the beach, one raising a banner while others erect a large cross. They face a group of Indigenous people who offer objects such as vessels and ornaments. Sailing ships sit offshore, and the coastline is dotted with figures under a partly cloudy sky.

”The human cost defies quantification,” says Hannah Skoda of Columbus’s discoveries | Credit: Getty Images

While Columbus’s expedition is rightly remembered as a seminal achievement, it also set off centuries of exploitation, oppression and hubris. The human cost defies quantification. As Europeans returned to the area, Indigenous populations were hit with diseases to which they had no immunity, notably smallpox. Local peoples were often enslaved, and patterns of slavery intensified even further over subsequent centuries with the development of the transatlantic slave trade. These ‘discoveries’ – still feted as such with little recognition that they weren’t discoveries for those who already lived there – marked the beginnings of colonisation.

There are alternative narratives of course – the exchange of foodstuffs and agricultural patterns, the opening of global trade routes and so on. But Columbus’s own diary is telling, even if it is a slightly dubious document. It bears witness to his sense of assumed superiority and extractive exploitative logic from the very first voyages: “In fact they took and gave everything they had with good will, but it seemed to me that they were a people who were very poor in everything.” More fool him.

Hannah Skoda, associate professor of medieval history at the University of Oxford

Rushing to the altar

One ill-judged marriage was all it took for King John to forfeit his empire

One year into his reign, King John was arguably the most powerful ruler in Europe. Not only was he King of England and Lord of Ireland, but he was also Duke of Normandy, Count of Anjou and Duke of Aquitaine. This continental inheritance was officially acknowledged in May 1200 by the king of France, Philip Augustus. A few months later, in August, John travelled to Aquitaine, where he married Isabella of Angoulême, the daughter of a local count.

A detailed illustration of a crowned figure wearing a gold, jewel‑studded crown and a sheer veil. The person has light skin, brown hair, and a red garment with a white ruffled collar. One hand lifts the edge of the veil beside the face, set against a plain grey background.

A modern engraving of Isabella of Angoulême, whose marriage to King John triggered the loss of his French lands | Credit: Bridgeman Images

John was 33 at the time of his wedding, his new bride probably not quite 12. But the problem as far as contemporary politics was concerned was that Isabella had already been betrothed elsewhere. Her hand, and her huge inheritance, had been promised to a powerful Aquitanian nobleman called Hugh de Lusignan, who reacted to his loss by raising rebellion.

When John retaliated, Hugh complained to Philip Augustus, who used the dispute as an excuse to resume the war against his Plantagenet rival. In 1204 the French king launched a devastating assault on Normandy and Anjou and by the end of the summer he had conquered both completely. John never managed to recover these lands, and they remained lost to the English crown forever. “You hear, lady,” said the king to his young queen, in a conversation imagined by a contemporary chronicler, “all that I have lost for you.”

Dr Marc Morris, historian and author specialising in the Middle Ages

Rome's misplaced trust

Betrayed by an ally, Rome marched into one of history’s most devastating traps

Rome had suffered military disasters before, but few were as avoidable, rooted in misjudgment or transformative in their aftermath as Varus’s catastrophic defeat in the Teutoburg Forest in AD 9. The defeat was so devastating that it halted Roman plans to conquer Germania and ultimately helped shape the political map of Europe for centuries to come.

Emperor Augustus sent Publius Quinctilius Varus, a senior Roman official, to govern the regions beyond the Rhine. In AD 9, he led three full legions of roughly 15,000 to 20,000 soldiers deep into the dense forests of Germania to put down what he believed was a small local disturbance. To guide him, he relied on a local leader named Arminius, who had once served in the Roman army.

A large greenish‑bronze statue of a warrior stands on a stone pedestal, holding a sword raised high in one hand and a shield at the side. The figure wears a short tunic, armour, and a winged helmet, posed triumphantly against a bright blue sky.

A monument to Arminius, whose deception led to Rome’s crushing defeat | Credit: Getty Images

What Varus did not know was that Arminius was secretly uniting several Germanic tribes against him. Instead of leading the Romans to a quick victory, he led them into a carefully prepared trap. Caught in unfamiliar, boggy terrain and stretched along narrow forest paths, the Romans were attacked repeatedly over several days. A torrential downpour turned the ground to a muddy mess, making their disciplined formations useless.

Varus’s misplaced trust and underestimation of the Germanic people ended with all three of Emperor Augustus’s legions wiped out and Augustus wandering his palace in Rome crying: “Varus, give me back my legions!”

Dr Jess Venner, Leverhulme early career fellow at the University of Oxford

The charge of the Light Brigade

A fatal miscommunication sends 600 cavalrymen to their deaths during the Crimean War

On 25 October 1854, a bloody battle took place outside the Crimean port of Balaklava. Lord Raglan, the British commander, ordered the light cavalry to ride out and harass Russian infantrymen who were attempting to seize British guns. His instructions were miscommunicated and the officers on the field thought he’d asked them to charge directly at Russian artillery. It was an – accidental – suicide mission.

More than 600 cavalrymen were blasted by cannon and musket fire on three sides. One soldier later said the experience was like “riding into the mouth of a volcano”. Although they reached the Russian guns, the Light Brigade was soon forced to withdraw under a storm of artillery, leaving more than a third of them dead or wounded.

A dramatic painting of a 19th‑century cavalry battle. Soldiers in colourful uniforms fight at close quarters on horseback, swinging sabres amid smoke, fallen men, and scattered cannon. Explosions rise across the hilly landscape in the distance.

The Charge of the Light Brigade “was an – accidental – suicide mission”, says Bob Nicholson | Credit: Alamy

Costly errors are not unusual in war. What made this monumental one so famous was that it played out in front of a journalist. The Crimean War was the first major conflict of a new media age, and William Howard Russell’s vivid report for The Times inspired Tennyson to pen The Charge of the Light Brigade, which established the attack as one of the most infamous mistakes in British military history and also immortalised the courage of the men who died:

“Theirs not to make reply,

Theirs not to reason why,

Theirs but to do and die.

Into the valley of Death

Rode the six hundred.”

Bob Nicholson, writer, broadcaster and historian at Edge Hill University

Invading Russia, twice

Both Napoleon and Hitler overreached – and the Russian winter ensured their downfall

By 1812, Napoleon Bonaparte was riding high. He had established France as the dominant empire in Europe, seeing off opposition from Russia, Austria and Prussia. Only Britain remained as a major threat to Napoleon’s overweening ambition, but so far it had been unable to dispute his dominance of the continent.

Then Napoleon decided to invade Russia. The ensuing campaign would be one of the most devastating in military history. In the space of just six months, from when it began in June 1812, almost a million soldiers and civilians perished. Fatally weakened, the French forces suffered a crushing defeat at the battle of Leipzig in 1813, following which Napoleon was forced to abdicate and was exiled to Elba. The end of all his hopes came in 1815 at Waterloo.

Soldiers in winter uniforms advance through deep snow, carrying weapons and equipment. Leafless trees and small evergreens stand in the background, with smoke or haze partly obscuring distant buildings and a military vehicle on the left, creating the sense of an active combat zone.

The German army en route to Moscow, 1941. Hitler’s decision to invade Russia would be his undoing | Credit: Getty Images

Fast forward to 1941 and Adolf Hitler was similarly enticed by Russia as the gateway to world domination. His invasion began well, with German forces conquering large swathes of Soviet territory, laying siege to Leningrad and reaching the outskirts of Moscow. But the onset of the brutal Russian winter halted his progress and enabled the Soviets to galvanise their resistance. It would prove a turning point in the Second World War, ultimately leading to the Soviet advance on Berlin less than four years later.

Which of the two was the greatest blunder? There’s not much to choose between them. But given he failed to learn from the lessons of the past, perhaps the prize should go to Hitler.

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Tracy Borman, author, broadcaster and chief historian at Historic Royal Palaces

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