Final Enemy, published in 1950 in Super Science Stories

“Final Enemy”
by L. Ron Hubbard

Publication date: September 1950

Original publication: Super Science Stories

Genre: Science Fiction

Story description: A threat to Earth from mysterious invaders responsible for killing millions of people on distant planets ends when, paradoxically, they find the invaders came from Earth.

Currently available as part of the Stories from the Golden Age series, in the title Greed.