Secession or civil war - how does the game decide?
Secessions and civil wars involve a rival party or parties breaking away from your faction. They are different - for example, a secession protects the player from further secessions or civil wars for a fixed number of turns; a civil war protects the player from these events until the civil war ends. When you get a civil war, there's a cut-scene video (with two lions fighting each other) at the start, and another (with only one lion) at the end.
Knowing how the game decides whether it's a secession or civil war could be useful. Sometimes players who want the 'The Die is Cast' achievement ask how to cause a civil war (as opposed to a secession).A player might want to use the fact that you're protected from further secessions and civil wars for as long as a civil war continues, by allowing the break-away faction in a civil war to survive.
I've seen different theories about how - when a rival party/parties break away - the game decides whether it's a secession or a civil war. Some players said that, if one rival party breaks away it's a secession, while if two (or more) break away it's a civil war. Others suggested that, if the rival party/parties have less than 50% influence, it's a secession, and if they have more than 50%, it's a civil war.
How do you think the game decides whether it's secession or civil war? Has anyone been able to find anything in the game's files which provides a definite answer?