Well, here is the biggest known case of butterfly effect -
**World War II** did not start with some massive machinations of world leaders. Rather, it culminated into a wide-scale butchery just because of a very small incident in June 1914.
Franz Ferdinand, the crown prince of Hungary, was going on a ride in a street of Bosnia, when his driver **mistakenly took a wrong turn**, and by chance bumped into a revolutionary named Gavrilo Princip.
The revolutionary, seeing the opportunity, instantly shot Ferdinand and his wife, who both succumbed to their injuries. Their death led to declaration of war by Austria-Hungary (supported by Russia) on Serbia, and the frenzy was soon joined by countries like Germany, France, and Britain due to several diplomatic treaties signed during that time, which blew into a full-scale world war.
If World War I had not happened, Versailles’s treaty would have never been made leading to Germany’s humiliation. Fanatics like Hitler would have never got the opportunity to come to power, and **World War II** could have been averted with six million Jews and 60 million other lives saved (estimated to be roughly 3% of 1940 population!). Also, Britain would have never drained its resources in financing the war, and there might have been three superpowers instead of just two, probably avoiding cold war, nuclear-arms race, and Vietnam and Korea conflict.
The outburst of war also had another butterfly effect on science. We would have never appreciated the intelligence of **Albert Einstein** if World War 1 had not happened.
Einstein needed mathematical proof for his **theory of relativity,** and to do that, he needed pictures of total solar eclipse, which was scheduled to take place in Crimea, then in Russia. He sent an expedition to the country for the same, but by then, **World War I** had erupted.
The appliances which the expedition had carried was confiscated by the Russian army, and Einstein waited for years for the war to be over. Naturally, he grew desperate and anxious, cursing his luck all through-out this time. One day, while skimming through his calculations, he realized he had committed some errors in his equations. He re-engineered his calculations, and sent a fresh expedition once the war was over. The pictures which finally arrived proved his theory correct.
If the ongoing war had not prevented the arrival of pictures in 1914, Einstein’s theory would have been surely proven wrong, and our understanding about cosmology, or origin of universe might have never reached this level. And of course, all talks of time travel may have remained complete fiction without any substance.
**And it all happened just because driver of Franz Ferdinand took a wrong turn!**