Clash of Star-Kings by Avram Davidson

Paperback. Condition: Good-/Good. 1983. Ace. Stock Image. Second Edition.

Set during the reign of the Aztecs in Mexico, two alien forces, dormant for centuries, enter a confrontation on a remote mountain that will decide Earth's fate.

The Great Old Ones benevolently ruled before the cruel Aztecs were shaped by the Huitzil, who came from the Evil Stars and taught the Aztecs how to conquer and demanded endless human sacrifice.