That's a pretty broad category, and a lot of books have been done on that subject, including books that focus on narrower aspects (such as certain genres, etc.). There have even been some fictional books (novels and collections) that examined that theme. Michael Moorcock's books often deal with that particular issue, especially such things as Blood and several of the Von Bek books.
This being the case... are you looking for something more scholarly, or from a layman's point of view; something that gets into the psychology of it, or is more general in approach? Any more information would help to get closer to what you want.....