I don't know how friendly or unfriendly previous empires were, so I'd like to read up more on it, but I honestly don't know what keywords I'd look for. Asking the one who made the claim for references seems like the best way for me to understand their comment better. Why do you expect me to provide arguments counter to theirs?
You want to look out for border regions, the small nations were other empires ended and went back and forth. You look for civil wars (empire lovers VS suppressed), cultural extinction attempts and empire imitators.. Aka small nations behaving atrocious to remain free by mimicry.. Sift through history and you get to know alot of empires that were and are worser.
