Might not be Nationstates official canon but this is for my empire...
Omnipotencia may not be the oldest empire out there, but it has skyrocketed past the levels of other empires in nearby galactic systems. They have conquered over 10 galaxies, and their advanced technlogy means they are able to conquer more in very short periods of time.
Omnipotencia has been reclassed as a Type-V civilization. Their main warship, The Omnisicent, is capable of scaring even the most formidable civs into submission. if that doesn't work, the countless fleets of starships and smaller warships will ensure there will be no more civ to scare.
I also keep forgetting how to spell civilization.