Collective memory is a thing created by society for things it deems important as part of its narrative and propaganda. We can collectively remember things going back centuries if it fits our narrative. WWI for example.

The opposite is true of things they want us to forget. Some things that's always a good time to remind people about.

Panama Papers - illegal tax havens for billionaires got exposed and the only consequence so far is the murder of the journalist who broke the story.
https://en.wikipedia.org/wiki/Panama_Papers

Tulsa race massacre - worth the wiki read.
https://en.wikipedia.org/wiki/Tulsa_race_massacre

Rodney King riots - https://en.wikipedia.org/wiki/1992_Los_Angeles_riots

The list is very, very long and I'll need help to compile anything resembling a decent one. So many things I've forgotten already, by design.