i like the idea of civil war, definately, but it should be much more fleshed out than it was in Civ2, IMO. First, capturing a capital shouldnt *always* be a trigger to civil war. There should be other, less predictable ones that are not completely dependant on war (for example, a religious Civ builds Copernicus' Observatory or something that would potentially really make the people angry, or a tax rate over a certain percentage for a long time, or being in disorder for a really long time perhaps... it should be extreme conditions that would result in civil war, but it shouldnt just be caputring the capital.)
Also, i always thought it was a bit silly in Civ2 that it would always be a rival Civ that would spring up when you took a capital. This is cool if the Civ that sprung up had just been eliminated by the city falling into civil war, but i think there should be certain "sub-civs" that civil wars generate for certain other civs. For example, in the ancient ages, if the Romans get hit by civil war, the new civ could be the Etruscans, if Rome gets hit by civil war in the industrial era, it could be the Vienesse. For Germany, ancient civil war could result in the Goths or Visigoths, medieval civil war the Bavarians, Industrial civil war the Austrians or Poles, and Modern could give East Germany or perhaps Lithuwania or Lichtenstein. France would have the Burgundians, a host of middle age civs.
Also, rival civs could foment civil war and rebellion in other civs, and the diplomatic attitude of those "new" civs would be reflected by your support (or lack there of). For example, if I'm fighting the Chinese, I can give gold to independance movements in China. Lets say China has civil war in the industrial era and Tibet breaks free. If my support had been sustained, the Tibetan envoy would be worshipful, if i didnt support them but had been at war with the mother country, they could begin furious. Of course, there would be middle ground: a tech or two or a few hundred GP could get you Polite / Gracious, whereas indifference could get you Cautious.
A few questions though: should these "sub-civs" have UUs and traits? Should subcivs even be in there? Am i out of my mind?
-john