[jimbob]

Quote: "2) After one planet "breaks away", then each other planet in the system is checked to
see if they join... All Rioting/angry planets join 100% of the time, unhappy/Displeased planets join 50% of the time, Indiffrent planets join 25% of the time (happier planets do not join)."

This I like. Simple ratios, very straight forward. Results in a nice cascading effect. Indifferent and displeased planets actually matter.

I'd add :
i) that any ships in orbit and troops on ground will decrease the probability of rebellion by a small arbitrary %
ii) if the planet contains aliens the probability of rebellion goes up by a significant but arbitrary %
iii) any troops on/ships orbiting a successfully rebelling planet defect to the rebels! (maybe a small % are loyal, so self destruct/disband?).

Thus, keeping control by military force is a large gamble. I think many military coups go something like this... the army is built up by a nasty dictator until they realize that they have so much power that they're really in control. Sometimes they grab power for the people but devolve into the power institution themselves. Usually they just grab power for themselves.