This idea covers politics rather than science or diplomacy.
I've recently read about the American Civil War, and just watched Captain America: Civil War (the latter being rather irrelevant and has little to do about this topic), and I've became interested in asking if there's any ideas about whether a part of your empire will secede depending on your political unhappiness or something. I've heard that this can happen in Spore where at least one of your planets can have a rare chance of seceding if the population suffers from unemployment or lack of entertainment.
I believe that it's likely this topic hasn't been discussed yet, but my questions would be, can a part of your empire secede if they do not agree with the direction you take? And if so, would the situation be able to escalate from simple peace, to a interstellar war? I understand if this thread belongs in a different sub-board.
EDIT: Wow, someone already liked this thread in 9 minutes?
We've thought a bit about this, and it fits in well with the kind of gameplay we (or I, at least) hope to see in all of the strategy stages. We've had some discussions about how to keep the game interesting and avoid the problem where you get a nation forming from a tribe of hunter-gatherers and then continuing on throughout the ages, one unbroken thread leading right to space stage; and it's clear that we need to design the game such that nations fall apart naturally, get conquered, get assimilated, etc; and we need to be able to do this to the player's nation over and over again without making the player upset that they keep 'losing'. For this kind of dynamic to provide deep gameplay, the breakup of a nation can't simply be arbitrary, but has to have some seeds that form within it.
So, all throughout the strategy stages, we'll be looking to model your nation not as some monolithic entity, but as a collection of various groups with often-diverging interests. As long as we can make that model flexible enough to allow part of your nation to assert independence, and defend itself with force if need be, then secession can and should happen.
CK2, for example, does a good job of having very obvious actors that can work at cross-purposes to each other, but I think that principle can be extended so much farther.
A good example would the the Civilization Forum Game that I'm running (http://thrivegame.freeforums.net/thread/318/official-thrive-civilization-forum-competition?page=1), which is meant to highlight the rise and fall of civilizations throughout history, but also the steady progression of technology and development.
Rather than playing a single civilization throughout all of history, you will play a succession of civilizations. If you want you can continue to play as a successor state of the same civilization when the original falls, and there will be plenty of breakup of large civs and cultural diffusion.