Triplanetary: by E. E. Smith

Hundreds of millions of years ago, two near-omnipotent alien races encountered each other, beginning a conflict that will shape the history of the entire universe. The benevolent Arisians covertly influence humanity, hoping to create a people capable of one day defeating the vile Eddorians, who are waging their own campaign for the fate of civilization on Earth. This sets the stage for a clash between the Triplanetary League of the inner solar system, the enigmatic pirate-scientist Roger, a...