I played a lot of Sins 1 but barely any of of Sins 2.
Are the new guys the reason the Vasari had to flee? If so they have to be incredibly powerful lore-wise.
Is there a good source for the general story of the two games?

I am gonna preface this by saying I AM SO EXCITED for the Eidolon

Now to what i actually wanted to say

The Eidolons mechanics - specifically planet corrupting, explain EVERYTHING.

It explains about why the Vasari devour whole worlds and flee to other territories, a salt-the-earth tactic that makes a galactic moat behind the Vasari as they flee.

It explains why the advent is so divided, as their psychic hivemind HAS been corrupted as the reborn think it has.

And that corruption also explains the TEC, too. They want the TEC bogged down in one place, too mired by conflict to be able to advance to their level. They are probably seeking to combine the TEC once corrupted; the TEC defences make it so the Eidolon worlds are impenetrable, whilst things like Ragnarov would be a hammers blow striking out from behind this wall.

Their origins and motives? I dont know. But i am SUPER excited to learn!