If you ask me? Mobile/WiFi internet… The way and amount of time we use our phones had changed A LOT since their diffusion. I guess the release of the iPhone changed our idea of what a phone is too
Edit: when I say modern world I’m referring to the last 50 years. So stuff like “the electricity” or “the telephone” doesn’t count.
One of the guys who invented the process for large scale production was Fritz Haber, to make explosives and chemical weapons. He’s also responsible for using chlorine gas on the battlefield in WW1. His wife was a chemist and an activist, who shot herself in the heart after learning about his involvement. Haber left within days for the Eastern Front to oversee gas release against the Russian Army.
He ended up saving more lives than he destroyed, but what a story.
There’s a really good section on him in the book, How to hide an empire - a history of the greater united states.
