41st Union Terran atrocity

In 4881, during the Back-Door battle, five Union fleets tried to circumvent Kermac Space and attack from the rear. They encountered a Galactic Council Thrall civilization, then known just as the Jellies.

The end result was Union battle ships obliterated sixteen star systems and 23 planets of the Jellies and affecting the extinction of the Jellies by destroying their incubation centers.