I'm not even sure Calsiim is directly responsible for the lower ranked devil nobles defecting to Yuigard's faction with the way he looks oblivious of what transpired, seemingly content with just sipping tea with his newfound room decoration tea mate. But they call him sly, so perhaps it really was his doing. I suppose this isn't the last we'll be seeing Belianna since she was named after all. That much screen time does not compute for a one-time throwaway mob character.
New lady Valentine is talking big things like she's going to be an actual threat, but I don't know about that. At least until her power gets tested in a confrontation with Flio. So it turns out the whole demon faction originally had ties to another world, the not-so-creatively named "dark world" where some of them probably originated.
So Gholl cut them off when he was demon king/"dark one", effectively turning the demon faction under him then into something like a new, independent nation. Just a little bit like how certain colonies in real life became independent countries from their parent country/kingdom. I suppose Valentine represents the desire of evil goddess Sterner and the other top brass to regain control of their, shall I say, wayward colony in this world.