To defend my point of view that capturing a capital shouldn't create civil war, I must point out in your (not so pc
) scenario chewy, you were talking about a seat of power being deystroyed. Ok, I see your point... maybe if the capital was glassed. But if it was captured by another empire, either the rebels would join the conquerors or they would Rebel against the conquerors... not their own empire, they've got other things to worry about. As far as glassing a capital, it should lower happiness empire wide (and if happiness will be a trigger for civil war, then it will do just what you want it to... just not automatically and EVERY time), and perhaps all production is cut by a third until a new capital is built.
Oh well, that's my 1/50th of a buck.