Inspired by @Fiachra's question in this post, I wanted to asked the broader tildes community: What are some of your favourite historic anecdotes or stories? The original question is more narrow, but I'm honestly curious to hear any fun or intriguing ones from any period of history.

Re-posting what I responded there:
OH man, time to share my favourite example of how one person being an asshole changed history: Shah Muhammad II of Khwarazm. The Khwarazmian Empire was roughly the Persian/Iranian Empire from 1077–1231. A massive, rich, culturally leading Empire at the centre of the Silk Road.

Genghis Khan, seeking to increase trade in preparation for his invasion of China, sent envoys to Khwarazm to ask to open trade. The Shah, in his supreme arrogance, decided these smelly Mongols insulted him by their very presence, and had them executed. Genghis, who very famously established the Imperial Mongol tradition of absolute protection for envoys, was furious. And yet, focused on his goal, he sent a SECOND group of envoys to demand an explanation and try to smooth things over. And the Shah executed them too. This pissed Genghis and his leadership off so much they paused the invasion of China, and launched a punitive expedition to conquer Persia/Khwarazm. I want to stress again that the records we have make it clear that the Mongols at this point had no interest in going further West. They were very focused on achieving victory over their arch-nemeses in China.

Within two years the entire Empire had fallen, the Shah was dead, and its fabulously rich cities torched and massacred. Following this, the Mongols realized they could continue to press on and ended up invading the rest of the Islamic world, famously including the destruction of Baghdad, the world's finest city of learning and culture at that point. The fall of Baghdad is widely considered to be the end of the Islamic Golden Age. Estimates of deaths in the Islamic World vary widely, but it is undeniable that many of the most populous and prosperous cities from the Mediterranean to the Caspian Sea were totally destroyed and depopulated. All because one jackass decided he couldn't be bothered to take some smelly Mongols seriously.

Also, I have no idea what to tag this, sorry lol.