Mankind first encounters and fights with the Orks and Eldar during this millennium. By this time, both of these xenos species have become superpowers in the galaxy, and humanity suffers heavy losses. WAAAGH! Skragjaw nearly reaches Terra before unknown heroes of this time manage to throw the Greenskin menace back for the first time in human history. It will not be the last.
Human Expansion & Scientific Advancement
For the rest of the age, Mankind spread across the stars, becoming widely dispersed and divergent. There is evidence of many wars, but none that threatened the stability of human space. Interplanetary trade was established and great fleets carried goods to and from the ends of the galaxy.
ca. Unknown Date.M22
Emergence of Human Psykers
As quick as Mankind's expansion had been, it was eclipsed by the speed of its collapse. The decline was so rapid, so utter and so nearly complete that little of those colonies or the civilisations they spawned remained. Speculation is rampant, but there are few facts. What is known is that human psykers are first mentioned towards the end of the 22nd Millennium, making a sudden appearance on almost every human world within a relatively short span of time.