And here’s the green-centred wedge. It’s Lovecraft-inspired.
Long before humanity’s time on Earth, the Primordials ruled the world. They were like the creatures of today, but larger and stronger and stranger. They were intelligent, very much so, but not in a way humans can hope to understand or communicate with.
Their time ended, but the marks they left on the world will never fade. The remnants of dead Primordials litter the plane, and everyone knows where to find at least a few pieces of the old world.
Their modern-day worshippers believe that The Eldest Thing, oldest and strongest of the Primordials, is not dead but simply sleeping. One day, if enough blood is shed, it will awaken and the world will belong to vast creatures that will wipe out the modern human race without ever noticing or caring about its existence.
Many people worship the Primordials, but few seek to bring them back. “Worship” in this case, mostly means paying appropriate respect to the memory of the creature whose bones tower over your home city and hoping that The Eldest Thing never wakes up.