So I joined the Princely Faction of my liege, considering I want to lower the CA so that I can gobble up my fellow Vassals again. Yet nothing happens. I can't declare "Lower CA" war, and neither can the Faction Leader (as far as I could see when I changed to him at least). Is it a plot or an ambition? Is it a random event that fires once the faction is Rebellious? Or how do I actually use a large faction in order to push its agenda?