what fact about our current world would freak people out if it were a newspaper headline a century ago?

The storm of the U. S. Capitol would be the most shocking one, probably, as nobody dared to do that.

Also, 9/11 events, nuclear/thermonuclear bombs, nuclear power plant disasters, many things.

Technologically, the fact that an everyday laptop can deliver tens of billions of arithmetic instructions per second is still mind-boggling to me.