Seatopia

Seatopia was an undersea kingdom created by the descendants of those who once inhabited Easter Island millions of years ago. Their civilization was sunk by a great earthquake but the Seatopians managed to survive and thrive beneath the surface of the Earth. They worshipped a beetle-like god called Megalon. All Seatopians looked like (and were likely biologically identical to) ordinary humans.

Although they were an inherently peaceful people, with no military, they became angered by atomic tests conducted by surface dwellers, and the then-current emperor, Antonio, appealed to Megalon to destroy the surface dwellers so the tests would stop. This plan failed, although Megalon's attack upon the Earth, short-lived though it was, made the humans think twice about polluting the Earth.