Ron Marz 
John Carter: Warlord of Mars Volume 1 – Invaders of Mars [EPUB ebook] 

John Carter, the Confederate soldier transported to distant Mars, must savehis adopted world from an adversary who is every bit his equal on the Red Planet: Captain Joshua Clark, formerly of the Army of the Potomac and now thestrategist for a species of star-hopping conquerors. While Carter and hisstaunch ally, the Thark chieftain Tars Tarkas, lead a legion of united Green Menand Red Men against the alien assailants, Dejah Thoris the princess of Barsoom is held captive by the bloodthirsty Clark in the fallen city of Helium. The "Invaders of Mars" storyline is cosmic-scale action and adventure, courtesy of Ron Marz, the groundbreaking writer of Green Lantern!