The Circassian genocide is the example that comes to my mind first. In my experience, most people, at least in Western countries, when they hear “Circassian”, they will immediately think I’m actually talking about Cardassians, a race of fictional aliens from Star Trek (or they’ll at least remark on how similar these words sound).
I also think the Milan Congress is an event more people should know about. This was a congress on Deaf education in 1880 that declared a ban on sign languages in schools, causing trauma and poverty and general harm to Deaf people for nearly a century until around the time of Stokoe’s research on ASL.
Really, the amount of history that people should know is abundant, but a lot of it is also very clearly more important to know if you live in a certain area, right?
Ah sweet! Man made horrors beyond my comprehension!