Avram Davidson

Here there be dragons... Earth was old, her riches gone. Her children too had left her, all but a few who lived peacefully off the land. And then came the Kar-Chee, to crack Earth open and suck out what remained of her richness, threatening the twilight of the old planet with an evil beyond anything that had gone before. With them they brought their servants, beasts so cruel and horrible that men could recall their like only from ancestral nightmares, and named them "dragons"...

Books like The Kar-Chee Reign

Your next favorite book is out there