OK, I confess that I did NOT vote on the issue of whether or not split nations should start in war or ever reunite etc etc-because I don't think things should be so ABSOLUTE, but should instead rely on in-game factors!
To put my argument into a more historical context, consider this: both Australia and the USA are former colonial holdings of Great Britain. Now, the USA split from Britain and war ensued-today, of course, they are the BEST of friends. Australia OTOH, was granted independance without a shot being fired, and we have ALWAYS been the best of friends with Great Britain! As far as unification goes, well a number of nations, like Italy for instance, have gone through periods of break-up and unification. Like I said, I think it depends on diplomatic and cultural factors-and the manner in which the breakaway occured. For instance, to use my historical examples above, I reckon that when a civil war is in the offing, your domestic advisor might come foreward and say 'Sire, the peoples of the _______ province are demanding their independance, what shall we do?' At this point, you COULD decide to let them go-in which case you'll get a reasonably amicable new civ on your border OR you can say 'No, dammit, they are part of our empire-send in the troops to quell the dissent!' If you choose the latter option, then the province almost certainly WILL break away (unless you can sufficiently alter their mood in the space of that turn) and the breakaway nation will be very hostile towards you, and may even declare war upon you!
Anyway, just some thoughts.
Yours,
Aussie_Lurker.