Finally, the Kssthrata gave up. The teraport had opened up literally millions of unexplored star systems, and as soon as a Kssthrata teraprobe returned with news of a suitable empty world, they packed everybody up and moved in.
EVERYBODY. Twenty-two billion peace-loving velociraptoroid sophonts packed up and moved from their homeworld, and managed to do so without letting the Ob'enn know they were doing it.
When the Ob'enn finally smashed Kssthrata defenses and pounded their planet's biosphere into damp gravel, there was nobody left there to care, and the Ob'enn never knew they'd been had -- at least not until they read the only-slightly-anonymized account of the largest retreat in known history in Milstrategist's Monthly.
The Kssthrata campaign against the dominant life form on their new homeworld was much less impressive, mostly since it was an oxygen-producing prokaryote.