Originally Posted by
Bramborough
From the Roman perspective (not sure what happens with other factions): One of your regions (single region, not a whole province) remains Roman, but rebels against YOU. This region is treated as a newly arising faction called "Senate Loyalists". In my case it happened to be Sardinia, just across the sea from Italia & Sicily. I'm guessing that the civil war faction will probably always spawn in an older region in or near Italia, rather than out on the fringe somewhere. And this does break up province cohesion, so it negates any edict you had, and may affect recruitment, depending on what buildings are in the rebelling town. For example, my most advanced fleet recruitment port was in Sardinia, so I didn't have access to recruit these vessels until after I retook that town.
In my case, I didn't lose control of any of my army/fleets (although I suspect this might happen if there's one actually stationed in the affected region). I did, however, lose all my Cornelii and Julii general/admirals, and had to replace them. The "Other Houses" general/admirals stayed loyal. So...six armies and four fleets (all 12 units each) insta-spawned in Sardinia, and proceeded to fan out toward Corsica, Sicily, and Magna Grecia from there. And they're all Roman troops, with access to the same level of units (in this case, legionaries with a sprinkling of veteran legionaries among them, with accompanying velites and equites). I did, however, have access to praetorians and 1st cohorts, but did not see any among the opposing legions.
So anyhoo, 6 armies and 4 fleets of Roman troops rampaging around the home provinces, yeah, it was a pain in the butt to deal with, and took quite a few turns to contain. I had enough power to do so, but had to call a lot of legions home so it took some travel time. Meanwhile, they ate up 3 provinces (Sardinia, Corsica, Lilybaeum) and *should* have taken Syracuse (not sure how/why they didn't, they were a step ahead of me and could've done so). They also landed a couple of legions in Italia, but by then my guys were closing in on them. In general, my sense is that the Campaign AI roughly marches toward Rome, although not necessarily in a straight line (thank goodness). And yes, you do have to deal with unrest and conquest public order penalties all over again when you retake those settlements (at least there's not a cultural assimilation though).
I don't remember exactly when it started, I'd say it took me 8-10 turns to get legions home, retake provinces, etc. As I type now, the civil war is still technically going on, but there's only a couple of small beat-up fleets I need to chase down and eliminate. I assume that once they're gone, the "Senate Loyalist" faction is eliminated and that's that. I don't know yet if there's some other event triggered like an internal peace treaty, or establishing the Empire (vice Republic) or whatever.
So bottom line, is it "hard" to deal with? Not necessarily, but harder than any other faction, I'd say. Derails your ongoing plans, takes time, causes some chaos on your core provinces, etc. The battle AI isn't really any smarter than for any other faction, but they are Roman troops, your units don't possess any inherent qualitative advantage over them, so they can't be taken lightly.