From the first D&D box set, the forward in the Men & Magic:
"These rules are strictly fantasy. Those wargamers who lack imagination, those who don't care for Burroughs' Martian adventures where John Carter is groping through black pits, who feel no thrill upon reading Howard's Conan saga, who do not enjoy the de Camp & Pratt fantasies or Fritz Leiber's Fafhrd and the Gray Mouser pitting their swords against evil sorceries will not be likely to find DUNGEONS and DRAGONS to their taste. But those whose imaginations know no bounds will find that these rules are the answer to their prayers. With this last bit of advice we invite you to read on as enjoy a 'world' where the fantastic is fact and magic really works!"
E. Gary Gygax, 1 November 1973
Tactical Studies Rules Editor, Lake Geneva, Wisconsin
No work of fan fiction or classic table top roleplaying is possible without the willing and active suspension of disbelief by the participants. Rather then endlessly debate the canonical sections of books I – V clearly quoted herein, it is best for the players and GM to expand upon the uncharted or unexplored areas of Barsoom.
“I might indeed be in some, to me, unknown corner of Mars, and this was very possible since during my ten years' residence upon the planet I had explored but a comparatively tiny area of its vast expanse.” (Gods of Mars, Chapter I).