Alternate History
Everybody copies each other. I read a series of books, about a Civil War regiment, that gets sent to another world to fight aliens. What happens? A guy writes a series about a World War 2 ship that practically has the same thing happen to it. Another writer wrote a book about a guy who travels back in time to give the South blueprints to an automatic weapon to win the war. However another time traveller stops him. Years later another writer about a racist group who gives the South AK-47s to win the war, and they do, but the South frees the slaves anyway. Yet another was a series of novels that had America fighting not just the South, but England during the Civil War, and of course that idea was expanded by another author who had America fighting England and France as well as the South during the Civil War. The what if/alternate history genre is likely the one genre of writing that people copy or the ideas are so few that nobody really notices. Some of it also has to be because pe...