The development of Nitrogen fertilizer. Kept the world from starving.
Bingo!
Everything else pales in comparison to this. The invention of the Haber Process in the early 1900's by Fritz Haber allowing the synthesis of ammonia fertilizer from natural gas and nitrogen is what allowed us to feed the world. Before that it took an inordinate amount of human labor to produce food, after chemical fertilizer became widespread a lot fewer farmers could feed a large number of people. This allowed labor to move off the farm and into industry while supporting a massive population boom. Without fertilizer there'd be about a quarter the current population on the planet and most would be engaged in farming to keep themselves fed.
“The development of Nitrogen fertilizer. Kept the world from starving.”
That’s considered a bad thing now..