Am I the only one who is tired of the plot that goes: “Well, you see, a long time ago there was a huge alien race that got pissed off that other people existed, so they decided to wipe everyone back to microbes every now and then.”
Sometimes, there’s a putative cause for it, as in Babylon 5, a series I love. But the whole Vorlon-Shadow war which was like, in the words of John Sheridan, “a couple of squabbling parents demanding the kids pick sides” was my least favorite part of it. Because it was like watching a couple of squabbling parents demanding the kids pick sides!! I mean, these were two demi-god-like races! I wanted the war to be over some transcendent disagreement or point of history Not Meant For Man To Know. Instead, it was basically American politics and personal pettiness (but I repeat myself).
David Weber did it a little better with his Achuultani in The Armageddon Inheritance, where the aliens at least have the excuse of being enslaved to an evil AI that can do self-maintenance for millennia.
At its worst, this trope takes the form it did in the game Mass Effect where the ultra-powerful Reapers sterilize the galaxy every million years or so because Reasons.
Folks, this trope is TIRED. And it’s an idiot plot. If the aliens are that powerful, why don’t they just create a fleet of robot ships to go burn the life off every planet that shows cholorophyll? Answer: because DRAMA! They always wait until humanity et al. develop the technology to play David to their Goliath and then get stopped. Also, how is it that the aliens always have this amazing social and political cohesion? They hang around, absolutely loyal to each other and content to do bugger all until the Evolutionary Alarm Clock sounds and reminds them it’s time to get back to slaughtering the Younger Races again.