The Imperium of Man is the apex of human society, spanning the majority of the galaxy and consisting of many hundreds of trillions of Humans. Under the ever-seeing eye of the Emperor, it's military might is unmatchable and it's Imperial Guard and Space Marines are the finest fighting forces ever to be assembled. Xenos scum and heretical traitors fall by the thousands before it's mighty guns, it's terrifyingly powerful planet-killing fleets of starships, it's armoured tanks and troopers.
For the Imperium of Man! Charge you dogs!
Short lived interstellar empire - also known as the Rule of Man or the second empire. Founded when the first valani empire fell to the terrans. Third Imperium dating sets this empire between the imperial dates of -2204 to -1776.
the -1776 date is arbitrary and is noted as the financial collapse of the central treasury.
This empire is the true Imperium of Man.
The Sylean confederation can trace it's origins to the failings of the Imperium of Man.