The film is largely based on A Princess of Mars, the first novel to feature John Carter. The novel was originally published as a magazine serial in 1912 and then brought out in book form in 1917. In the novel John Carter is an American Civil War veteran who is miraculously transported to Mars, known to its inhabitants as Barsoom, where he learns that he is the only person capable of saving the planet which is soon to die off from war and natural reasons

On a side note the orchestral/medieval (for lack of any other description) type of rendition of Zeppelins Kashmir makes a cool sound track.

Official John Carter Webpage

Another trailer for John Carter