Complex sentence: On Mars, which its natives call Barsoom, Carter encounters both formidable alien creatures resembling the beasts of ancient myth and various humanoids and finds his true calling in life as a warrior-savior of the planet's inhabitants.
Split into simpler sentences: On Mars, which its natives call Barsoom, Carter encounters both formidable alien creatures resembling the beasts of ancient myth and various humanoids. He finds his true calling in life as a warlord who strives to save the planet's inhabitants.