Which logical fallacy is used in the text?
Don't talk to me about the legacy of Napoleon! If you're not a professional historian, then there's no way you know anything about it.

 - false dichotomy: an argument that presents only two choices when more options exist
 - false causation: the assumption that because two things happened together, one caused the other
 - guilt by association: a negative association intended to discredit someone or something
The text argues that either you work as a professional historian or you don't know anything about history. However, people can be knowledgeable about history even if it isn't their profession. Furthermore, just because someone studies history, it doesn't mean that person is knowledgeable about all aspects of history. This illustrates a type of logical fallacy known as a false dichotomy.