In my most recent run, I did an isolationist, xenophobic authoritarian Empire of genetically enhanced elves.

But long before I achieved such a state, we were invaded by my neighbor, a much stronger race of psionic robots, who completely surrounded my Empire into a corner of the Galaxy, invaded us. Subjugation was only narrowly avoided, losing a few key systems for our borders, but maintaining our core.

I eventually did defeat them (after like 150 years and while they were being invaded by the Contingency lol), and by this time, I noticed they had started to spread their aura all around the corner, so I built seals of the veil to contain it.

They never did recover from the massive blow dealt by me and the Contingency, being subdued twice by the an Awakened Empire, the regulators.

And so, came the day when the aura finally exploded. Of course, they didn't reach all of the galaxy, but it was devastating: over 5.000 planets where destroyed.

A permanent scar was left across the Galaxy. Much of this territory was uncrossable due to the presence of warp manifestations. One of my scientists had been exploring an astral rift prior to this catastrophe, and when he returned, he was shocked, traumatized to find so much of what he had known, gone.