| "Challenged" means "Someone asked their local public or school library to ban this book". "Banned" means said library actually did so. Given that it's the ALA, the American Library Association, tracking this, it is indeed one that is USA-specific.
As to why some of these were challenged/banned, just ask yourself "Is there some possibility that someone, somewhere, would be offended by this, reasonably or not?" If the answer is yes, that's why. Note that the answer will be yes for almost any book in existence.
And like Admiral Maxtreme, I do find it ironic that "Fahrenheit 451" is on the list. Not surprising, though. |