THE HEART ATTACK THAT SAVED THE WESTERN WORLD
You know how every comic book villain and James Bond mastermind has some convoluted plan to take over the world? Totally ridiculous, right? The entire world? Come on. Nobody can possibly hope to do that.
Or maybe real villains just don't think big enough, because it can be done. In fact, if it weren't for a well-placed heart attack, it probably would have already happened.
The Ridiculous Coincidence
Welcome to Central Europe, circa mid-13th Century. A few years ago, you got word of some powerful distant nation, led by a guy named Genghis Khan, was destroying the hated Muslims. "Great!" you said. "The enemy of my enemy is my friend! What could possibly go wrong?"
Then things started getting sketchy. You heard about this mysterious army utterly annihilating Russia. Hey, that's not right! Russia is Christian! They're Orthodox heretics, sure, but they're still Christians.
Then one day, you finally meet this friend. Except, instead of bringing you Funyuns and Mountain Dew, he's here to slaughter you and everything you hold dear.
Folks, this was the Mongol Invasion of Europe. And shitty Europe, with its clunky knights and piss-poor peasantry, could do absolutely nothing to stop it. The Mongols, led by Genghis Khan and later, his son Ogedei, defeated the armies of such greats as Hungary, Austria and the Holy Roman Empire. They utterly plundered Poland (thank God that country never suffered again), and set their sights on the next densely populated nation: Germany.
Then, the Mongolian leader, Ogedei Khan, died. And everyone had to go back to Mongolia.
Why? Because Mongolian cultural traditions required everyone to go back home when a new khan ascended. Everyone knew that Ogedei's son Guyuk was going to succeed him, but they all had to go back to Mongolia and ceremonially "vote" for him anyway--or vote for someone else, and probably get their face skewered.
And How Did it Change The World?
More than you might think, actually. One recent book speculates that the Mongols' destruction of the Islamic heartland, and their comparative non-destruction of Europe, was what allowed the West to become the power center it was.
After they were done piling skulls into pyramids, what the Mongols basically did was connect the world. New trade routes opened up, and new contacts were made between the major centers of population.
So while China and the Middle East were getting their shit burned, Europe was gaining new contact with the East. This, in turn, motivated the Age of Exploration. Hence why the West has nukes and computers and technology today, while everyone else has goats and carriages. Thanks, Mongolia!