Gods of Mars

After John Carter arrives on the red planet, a group of Green Martians navigating the River Iss faces a brutal ambush by the mysterious Plant Men. The only survivor, Tars Tarkas—the Jeddak of Thark—embarks on a quest to find Carter in the fabled Valley Dor. Together, they uncover a shocking truth the Therns, a race of white-skinned beings who claim to be gods, have long manipulated the Barsoomians by promoting the pilgrimage to the Valley Dor as a path to paradise. However, this journey often leads to death at the hands of monstrous beasts, with the fortunate few falling into Thern enslavement. (Summary by Wikipedia)