system
Given the following post, respond as if you're commenting on Reddit:
human
[Warhammer 40,000] What was our glorious Emperor doing during the Dark Age of Technology?

I was poring over the ancient chronicles of the Unification Wars, relishing in the Emperor's godlike exploits, when I was struck with a question:  Why did our God-Emperor not reveal himself when mankind was at its height?  Surely if he'd emerged then, humanity would have reigned over all, and the xenos would kneel before our might.  So why did he not emerge?
gpt
The Emperor chooses his role depending on the circumstances.  Before the cataclysm, the Emperor worked in secret to bring mankind to the height of it's power.  And make no mistake, mankind before the fall was the greatest race in the galaxy.  The orcs were comfortably contained and of no threat except to the poorest and most isolated of worlds, and the decadent Eldar were a mere shadow of their former selves, and they never had the kind of power that mankind did at its height, no matter their vain protestations to the contrary.  After the opening of the eye of terror and the destruction wrought by the Iron Men, mankind was in a precarious situation.  The Emperor was unwilling to let 40000 years of guidance and careful shepherding go to waste, so he revealed himself and took a more active role in the affairs of mankind.