Many writers of genre fiction rely on their audience having read fewer history books than they have. I saw people online calling George Lucas a prophet for depicting the decline of the Republic in the Prequels, but he really just read a couple of books about Ancient Rome. And dragons and zombies make the premise of "what if the Mongols invaded during the War of the Roses" a lot more exciting.

Originality is overrated though, so I don't mind. One of my favorite science fiction novels, The Stars my Destination by Alfred Bester, is transparently based on The Count of Monte Cristo.