A Princess of Mars was the first serial novel published by adventure writer Edgar Rice Burroughs (the Tarzan guy) almost exactly 100 years ago. It’s a classic tale: Civil War veteran is mysteriously transported into the midst of two warring cultures, of course, with a beautiful woman to be saved. Hmm, countless sci-fi films and more than a few Western flicks have borrowed that theme. Most recently and notably, James Cameron has said that A Princess of Mars (which he read as a child) was his inspiration for Avatar. Here’s the problem: Once so many others have copied it, the original feels — oddly enough — derivative. Despite all that, Disney gambled that Princess had enough life left to kickstart a new franchise.