If a computer player's capitol is captured, but that player still has other cities left in its civilization, a civil war will break out if all of the folowing conditions exist:
* There is at least one civilization not in the game that can form a "rebellious" faction (i.e., the Babylonians have been wiped out, so the Zulus are waiting in the wings)
* There are greater than four cities remaining in the civilization that has just had its capitol captured
* The civilization that has just had its capitol captured is larger than your civilization
When a civil war occurs, the civilization that just lost its capitol will get a free palace, instantly creating a new capital city. The "rebel" civilization will also get a free Palace and the cities of the "old empire" will be divided between the two warring factions. (Wilson and Emrich, 1992:350-51)
Wilson, Johnny L. and Emrich, Alan.
1992. Sid Meier's Civilization or Rome on 640K a Day. Rocklin CA: Prima Publishing.