[ClumsyPilot]

> plurality of citizens are horrified enough that they can put public pressure on a public figure powerful enough to force structural change

So basically only 9/11 or Perl Harbour would qualify.

[AndrewKemendo]

Great Depression takes the cake here

Pearl Harbor for sure

Ozone Layer hole and the subsequent Montreal Protocol (banning of CFC) was notable in its speed and efficacy

9/11 is questionable - the response was bad and counter productive so I’d say no it doesn’t count