20 Human Mistakes That Changed History Forever

Welcome to WatchMojo, and today we’re looking at the most consequential blunders throughout human history.

Kim Jong-nam[a] Goes to Tokyo Disneyland

Kim Jong-nam was once the heir to the North Korean dictatorship, until 2001 when he made an embarrassing attempt to visit Tokyo Disneyland. Traveling on a fake Dominican Republic passport bearing a Chinese name, Kim was arrested upon arrival in Japan and deported to China. The incident deeply embarrassed his father, Kim Jong Il, and caused him to be shunned by his family. Ultimately, his younger half-brother, Kim Jong Un, took over from their father. In 2017, Kim was assassinated in Malaysia, and it was later revealed that he had been a CIA informant. He also supported reform and free market policies, which apparently contributed to him being passed over. Had he never attempted that fateful trip, perhaps North Korea’s trajectory might have been different.

Byzantine Refusal to Hire Orban[b]

The Roman Empire’s final two centuries were their most difficult. By 1452, the Ottoman Empire already had its eyes on Constantinople, which prompted Hungarian siege engineer Orban to offer his cannons to the Romans. Unfortunately, they couldn’t afford his services or provide the materials needed to construct his weapons. So Orban took his business to the Ottomans, who happily took him on. He crafted the basilic, one of the largest cannons in history, requiring 90 oxen and 400 men to transport it. Its cannonballs, each weighing 1200 pounds, devastated the Theodosian Walls, which were impenetrable for about 800 years prior. The Ottoman Sultan also carried warships across the land, bypassing the harbor’s great chain, and giving them another huge advantage.

Titanic Sinks After Iceberg Warnings Are Ignored

Many mistakes were made that caused the Titanic to sink, so it’s difficult to pinpoint just one. Perhaps the most consequential, though, was turning “hard-a-starboard” when they spotted the iceberg, which extended the collision, creating a large gash that flooded five compartments. Had they struck the iceberg head-on, the bow would have been crushed, but only one or two compartments would have flooded. In such an event, the ship could have survived, as it was built to still float with up to four flooded compartments. Also, it carried only 20 lifeboats, enough for about half the passengers. The primary mistake that night was ignoring iceberg warnings and maintaining a high speed throughout. Changing just this one decision could likely have prevented the accident.

Mexico Attacks the Alamo

In 1836, the Texas Revolution was underway, with the Anglo-American residents of Texas fighting for independence from the Mexican Republic. They were successful, winning 10 years of independence before joining the United States in 1846. During the war, Mexican forces under General Antonio López de Santa Anna[c] laid siege to the Alamo. After 13 days, roughly 1,500 Mexican soldiers launched a decisive attack, overwhelming the garrison of about 200 Texians after three attempts. It was a pyrrhic victory though, as the merciless bloodshed inspired many to join the Army, hoping to take revenge for the loss of their fellow Texians. Mere weeks later, a now fortified Texian army attacked the Mexicans by surprise in the Battle of San Jacinto[d], decimating them in just 18 minutes.

Trojans Bring In the Horse

This was a mistake so monumental, it became a metaphor for deception that is still widely used today. The ancient city of Troy was first destroyed around 1200 BC, and again by archaeologist Heinrich Schliemann[e] in the 19th century. According to legend, the Greeks built a giant wooden horse, hid soldiers in it, and presented it to the Trojans as a gift. Believing it to be a symbol of victory, the Trojans brought it into their city, only for Greek soldiers to emerge and decimate Troy. The tale’s authenticity remains heavily debated, with no direct evidence. However, oral history played a central role in the ancient world, which preserved surprisingly truthful elements, suggesting that this tale may have been inspired by real-life events.

Caesar Ignores Warnings

Julius Caesar is most famous for sowing the seeds of the Roman Empire, enslaving and slaughtering millions of Gauls, and giving the month of July its name. He was eventually assassinated in 44 BC, which shouldn’t have come as a surprise, since he was given several warnings about it. All of these were dismissed, leading to his death in the Senate, where he was stabbed 23 times. A soothsayer warned him to beware the Ides of March, the eventual date he was killed. His wife Calpurnia had a dream of his death, and insisted he stayed home, but he dismissed her fears. Ultimately, his trusted friend, Brutus, convinced him to come in, which turned out to be the dictator’s final mistake.

Mao’s Great Leap Forward

Mao Zedong[f] was the founder of Communist China, who became leader of the CCP during the Long March, a pivotal event in the Second Sino-Japanese War. After Japan’s defeat, he sought to industrialize China, and finally recover from the century of humiliation. He believed rapid industrialization would help them catch up to the West, but it turned into a catastrophic failure. The plan was overly optimistic, and resulted in mass famine and an economic collapse. By 1962, Mao faced criticism for his policies and was sidelined at the Seven Thousand Cadres Conference. This didn’t last long though, as just four years later, he kickstarted the Cultural Revolution, which allowed him to reclaim full control of the nation.

NASA Ignores Challenger Warnings

In 1986, NASA launched the shuttle Challenger, which tragically exploded only 73 seconds after liftoff. The event occurred during a cold morning, which caused the ship’s rubber O-rings to stiffen, leading to a fuel leak that ignited the vessel. All seven crew members perished, marking one of the darkest moments in the history of space exploration. Months earlier, several engineers, including Roger Boisjoly[g], had warned of an impending failure due to the O-rings’ vulnerability to cold. Boisjoly even wrote a memo outlining this issue, but his concerns were completely ignored. Although a team was formed to address the problem, they lacked adequate support, and the launch proceeded only to end disastrously, like Boisjoly predicted.

America Escalating Tensions in Vietnam

The United States entered the Vietnam War following the Gulf of Tonkin incident, where North Vietnamese forces allegedly attacked the U.S. Navy in international waters. The event was framed as an unprovoked attack, but later evidence showed otherwise. While the first attack remains debated, the second one was entirely fabricated. It devolved into a brutal war, which dragged on for years, causing thousands of American and Vietnamese deaths. Along the way, the United States committed atrocious war crimes, such as the My Lai Massacre[h]. Ultimately, the war ended in failure, all spurred by an incident with very little evidence.

Angering Genghis Khan

Many words can be used to describe Genghis Khan, one of history's most successful conquerors, but “cool-headed” isn’t one of them. In less than two years, Genghis annihilated the Khwarazmian[i] Empire. While there were a variety of factors that contributed to this invasion, the main one was an insult to his ambassadors. In 1218, the Khan sent a caravan to the Empire, who were arrested and executed, on suspicion of being spies. When Genghis sent diplomats to deal with the situation, the Khwarazmians refused to comply and beheaded the chief envoy. By 1221, their empire was shattered, and they had suffered somewhere between two and 15 million casualties. Maybe think twice before you insult one of history’s most ambitious conquerors.

Forgetting About Time Zones Hamstrung the Bay of Pigs Invasion

During the Cold War, the US backed numerous coup d'états around the world. While several of these succeeded in installing new regimes, attempts in Cuba failed spectacularly. Worried about Prime Minister Fidel Castro’s communist policies, in 1961 the CIA orchestrated the infamous Bay of Pigs Invasion - landing Cuban counter-revolutionaries on the country’s southwestern coast. However, an obvious paint job on a B-26 bomber, disguised to look Cuban, gave away US involvement to the world - leading President Kennedy to pull back air support. A few days later, a last ditch bombing raid flying out of Nicaragua was botched when bombers were caught without their escort of fighter jets. Embarrassingly, someone had forgotten the one hour difference between Nicaragua and Cuba.

Fleming Left Bacteria Out on His Bench

Scottish physician Alexander Fleming was a brilliant researcher, most famous for his work on bacteria, as well as THIS accidental discovery. While researching the bacteria Staphylococcus in 1928, Fleming left out culture plates on a bench in his workshop over the weekend. When he returned, he observed that fungus had grown on the dish. In the areas close to the fungus, the bacteria had been eradicated! The mold led to the creation of the first antibiotic, Penicillin. Without Fleming’s mistake, the history of medicine in the last century would look very different and many who lived may have died instead.

Chernobyl Nuclear Disaster

Chernobyl’s meltdown was the most destructive nuclear disaster in history, and could have been completely avoided if the proper procedures were followed. The disaster was immediately caused by a safety test, which was meant to be carried out during the day, with a trained crew. Instead, the untrained night crew did the test, with very little time to prepare for and properly carry it out. The Soviets were also secret about their nuclear technology, withholding important information from operators and engineers, who should have understood them. After the explosion, further mistakes were made, like the nearby town of Pripyat not being evacuated until over a full day later. It was the perfect storm of mistakes, leading to one of humanity’s worst disasters.

A B-Day Helped Lose D-Day

On June 6th, 1944, the Allies launched an ambitious operation to retake Western Europe. Known as D-Day, the first landings occurred on the beaches of Normandy, France. The casualties were high, but the operation granted the Allies a foothold that would eventually lead to victory on the Western Front. However, things could have gone very differently. The Germans’ most accomplished general, Erwin Rommel, was in charge of defending the Atlantic Wall against an invasion. However, he’d decided to take leave, as the 6th was his wife’s birthday, and German meteorologists had mistakenly predicted storms for another few weeks - making a seaborne invasion unlikely. Had Rommel been in command, the Allies may never have gotten a beachhead to retake France.

Russia Sold Alaska

During the 19th century, the Crimean War caused several countries to begin exerting pressure on Russia through blockades of their sea routes. Because of this, they were unable to properly supply their largest overseas territory, Alaska. To offset this, in 1867, Russia sold the territory to the United States for 7.2 million dollars. While it may have been a smart move at the time for Russia, in retrospect, it’s often seen as a mistake, as the gold and oil discovered in Alaska far exceeds the value it sold for. Not only that, but Russia having a foothold in the North American continent would have caused the Cold War to play out very differently.

Napoleon Invades Russia

In 1812, Napoleon famously declared war on Russia, citing their refusal to comply with the Continental System. He brought around half a million soldiers from all across Europe to the border, and proceeded to march them to Moscow. The Russian defense was confused, with no planned resistance, with their eventual scorched earth tactic being largely improvised. At the Battle of Borodino[j], Napoleon abandoned his usual cunning tactics and ordered a direct assault instead. The French won and Moscow was taken, but Little Boney never received the peace deal he expected. Eventually winter took hold, and Napoleon embarked upon one of history’s most disastrous retreats, costing him his army and, ultimately, his empire.

Hitler’s Invasion of Russia

A British soldier’s choice to spare the future Fuhrer's life during WWI turned out to be a HUGE blunder. But we’d argue that the most dramatic mistake involving Adolf Hitler was one he made himself. Despite signing a non-aggression pact with Russia, Hitler still considered Joseph Stalin and the Soviet Union his enemies. In June of 1941, the Germans invaded Russia. Despite committing the largest invasion force in history, the Germans were unprepared for the Soviets’ scorched earth tactics or the bleak Russian winter, and they experienced over half a million casualties. The offensive split and depleted the German forces, and put Russia on the side of the Allies, which likely lost Hitler the war.

A Wrong Turn Started WWI

One of the most famous killings of all time, the assassination of Austro-Hungarian Archduke Franz Ferdinand is usually credited with being the catalyst for World War I. But what some may not know is that it could have been avoided, if not for a wrong turn. The archduke had already survived one assassination attempt with a bomb by the same group while visiting Sarajevo. On the return journey, the archduke’s drivers, who spoke Czech, couldn’t understand their directions for a new route, and took a wrong turn. When they stopped to reorient, it was right next to one of the assassins who promptly pulled out a gun and shot both Ferdinand and his wife.

Treaty of Versailles Harsh Terms

The Treaty of Versailles was a deal signed in 1919 at the end of World War 1, which mainly focused on weakening the German Empire. Despite the Austrian-Hungarian Empire being the main instigators, sending a harsh ultimatum to Serbia, the victorious powers primarily blamed Germany. They had to accept full responsibility for starting the war, and were made to pay enormous reparations. This crippled their economy, and fostered resentment towards the victorious powers, which eventually led to Hitler’s rise to power, and World War 2. If the Allies had adopted a less punitive approach, like the U.S. did to Japan after World War 2, the devastating second war, and the rise of Nazi Germany, might have been alternate history.

Christopher Columbus Was Bad at Math

This Italian explorer was long portrayed as a hero, and the “discoverer” of the Americas. Nowadays, a lot more attention has been paid to his brutal treatment of indigenous peoples. But his most celebrated feat - sailing across the Atlantic Ocean in search of Asia - actually came about due to his mistaken belief that the Earth is a lot smaller than it really is. He arrived at this conclusion by using a mishmash of different estimates, as well as his own erroneous beliefs. If not for Spain’s dire need for spices, he probably never would’ve gotten a single ship, much less three.

What do you think was the most impactful mistake a human ever made? Let us know in the comments below!

[a]https://forvo.com/search/%EA%B9%80%EC%A0%95%EB%82%A8/
[b]ore-ban https://forvo.com/search/Orban/hu/
[c]https://forvo.com/search/Antonio%20L%C3%B3pez%20de%20Santa%20Anna/es/
https://forvo.com/search/texian/
PEER-ick https://www.dictionary.com/browse/pyrrhic
[d]san hah-SIN-toh https://forvo.com/word/battle_of_san_jacinto/#en
[e]https://forvo.com/search/Heinrich%20Schliemann/de/
[f]mao zahdoong https://forvo.com/word/%E6%AF%9B%E6%B3%BD%E4%B8%9C/#hsn
[g]beaujolais https://youtu.be/1jPP7Ks6Rhk?si=rPnJpHmcQv3vt3f-&t=1789 https://youtu.be/DB8iYf_857U?si=kgEeTbn922yJw7qV&t=216 https://youtu.be/KwV2datnyb0?si=kRmNFurXcIpgMQZv&t=29
[h]mee lye https://forvo.com/search/My%20Lai/en/
[i]kwuh-RAZMEE-in https://youtu.be/92-440OR2ik?si=zoJn2fSHMF55mIPS&t=71
[j]BORO-DIN-oh https://forvo.com/word/%D0%B1%D0%BE%D1%80%D0%BE%D0%B4%D0%B8%D0%BD%D0%BE/#ru