(6x24) The War of Antiquity: Part 2, Episode 3
The Berol eventually redevelop technological civilization, and in time attain space travel. Slowly exploring their star system, they eventually find in close orbit to their star the time dilation machine that is isolating their star system from the rest of the universe.
Turning it off, they find their forever-black sky suddenly filled with innumerable stars, and though they can't initially see them, the fleet of Ehrban science ships that have been monitoring the time-dilation experiment for, from their frame of reference, mere moments, but to the Berol, since before the dawn of time. This larger cosmos which challenges their entire view of what they thought of as the universe, in which they were the sole inhabitants surrounding the only star which, it was claimed, was the creation of their God-Emperor himself.
At the God-Emperor's direction, the time-dilation device is quickly turned back on (or from the Berol's perspective, the outside universe is "turned off"). All of Berol civilization is then repurposed with the singular goal of destroying the challenge to their orthodoxy: in other words, they declare war on the entire rest of the universe, whatever that should amount to. It'll have to go.
Next: The War of Antiquity: Part 3, Episode 1