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[Warhammer 40K] What was the Imperium doing for 18,000 years?

Even the most pessimistic predictions place the Singularity around 2100, by 10,00 AD the Imperium should have been so far above everything in the galaxy that there was absolutely no threat. Did humanity just sit around for 18,000 years until big wars happened?
gpt
The Warp Drive is actually listed as not being invented until the 18th Millennium, so before that humanity probably traversed the stars in large sub-light colony ships. The Warp Drive signified the start of major human expansion into the galaxy and also the start of the Dark Age Of Technology, which lasted from the 18th through to the 25th Millennium. The Dark Age was the peak of Mankind's power in the galaxy, a time of wondrous and fantastical technologies that have all been lost to the ages. Around M25, the Men Of Iron, AI's that we're built to serve humanity, all rebelled at once, almost wiping out humanity and plunging it into the Age Of Strife, however, the humans eventually triumphed but all remaining human colonies were pretty much severed from each other. Around four to five thousand years later, the Emperor would reveal himself and begin the Great Crusade, which then led onto the Horus Heresy, and so forth. The Imperium itself was not actually formed until the Emperor had united all of Terra, and it is not known what humanity referred to itself as before the formation of the Imperium.