the printing press was not a 20th Century invention . . .

Regardless, without it, our existence is very different and this discussion doesn't exist.

For the 20th century, The nuclear bomb, insulin, 1st World war probably rank about even. It was the most environmentally devastating century in the history of the world (non astrological). Lot to be proud of and lots to be ashamed of at the same time

this discussion is not "Why does this topic exist?" -- it is "What event in the 20th Century yadda yadda . . . " You could just as easily argue that Moses leading his people out of Egypt was the greatest event in the 20th Century.

two of those are not events, but thats splitting hairs. environmentally devastating is all well and good (not really), but why was it environmentally devastating?

what about the holocaust? that changed the lives of many many people as well.

Mine was pivotal in ending it.

Bill Clinton getting a BJ.

I only count two people that affected.

My vote is for the invention of the solid state transistor which made the modern world possible.