I didn't even try to count all the books about the Civil War and World War II, two broad topics that may never lose their appeal to those who enjoy reading about military history. I happen to be reading an excellent book about World War II myself.
I understand the attraction of each of these subjects because I own several books about each of them. I once got rid of a couple of my Churchill biographies because I thought had too many, but I still have five of them. I also seem to be overloaded with biographies of Theodore Roosevelt, Thomas Hardy and, of all people, Ivan the Terrible. We just can't seem to learn enough about certain people and certain events of the past.