The final scene for the BattleTech campaign I got out of a short novella published in Analog. I remember reading the last three parts at the CSUS library when I was a kid. A human colony on a distant planet finds some ruins. They are attacked by some sort of military force, I think another human faction. The heroes, who are investigating the alien ruins, find a control room and activate machinery whose side-effect is to destroy the enemy forces.

But what's the machinery for? The mystery leads them to some sort of transportation device which leads them to an alien planet, long dead. As the heroes contemplate the devastated ruins, stark in the twilight, they can see out in space, the remains of a half-built Dyson Sphere. Apparently the dead race had been involved in a losing war, and as one of the last desperate measures they wanted to hide their solar system. The Dyson Sphere would emanate the energy of a red star, effectively hiding the yellow sun and inner planets. But they ran out of time, and left these ruins.

That's the kind of backstory that drove the BattleTech campaign, even though it barely showed in the actual campaign. So now, since I can no longer rely on an epic premade Romulan campaign, I have think of something momentous to drive the campaign. And I think I may just have thought of an idea...