Quote Originally Posted by Knot_D View Post
It's the Ancients that want to sacrifice themselves to save their world by primal, but Venat stopped them and sunder the world to stop their nonsense... (Correct me if I'm wrong)
From what was implied slightly (and we probably could have understood more if a certain zone wasn't 90% devoted to fan service) is that the influence of Meteion was suggesting the populace sacrifice half of themselves - again and again - to sustain Zodiark. While we see that Zodiark was holding it back just fine without more sacrifices, I sort of assumed it was that it was the direct result of the Song's influence causing people to double down until no one was left.

SE didn't clarify or justify it, but that was my final interpretation of the cinematic. Why Venat wasn't influenced and why the Unsundered wanted to continue the cycle (sacrifice all those on the shards) I have no idea.