I think the most prominent examples would be: Nazis (obviously), Stasi / DDR / GDR, Chile (Pinochet) and the dictatorship in Argentina; but in the last century

I think the most prominent examples would be: Nazis (obviously), Stasi / DDR / GDR, Chile (Pinochet) and the dictatorship in Argentina; but in the last century there were many more examples, be it in South America, Africa or eastern Europe. Wikipedia has a list of historical secret police: https://en.wikipedia.org/wiki/List_of_historical_secret_police_organizations https://en.wikipedia.org/wiki/List_of_historical_secret_poli... -- Current examples that are still alive and well could be the various GCC states, but especially Saudi Arabia there; the UK and the US to some degree each (both are obviously full-blown surveillance states at the very least; and it can be reasonably argued that (divisions of) the FBI and some other agencies qualify as a secret police) in the western hemisphere; Russia.