This did happen in the Call to Power games: an unhappy city would riot, but when a city revolted, it broke away and declared independence. A new civ name and leader were chosen at random, and the new leader invariably hated the parent civ (understandable, since that civ's misrule was what sparked the revolt). The problem was, those breakaway civs inevitably started as just 1 city - so they were usually quite easy to recapture before they could expand and grow strong. If such a system in implemented in Civ 5, it should allow for 2 or more neighbouring cities to break away simultaneously, and form a single new nation. This would be basically identical to the existing colony system in BTS - except that it would happen against the player's will, creating a new enemy instead of a new vassal. Good idea. Also, wildlife and biodiversity should be important. Civ 4 already has dangerous wild animals, and animal resources; why not add various "neutral" animal populations to the terrain graphics, with different species on diferent landmasses? Developing a tile with farms, cottages, lumbermills, windmills etc wouldn't necessarily eliminate the wildlife; there should be a certain % chance of losing it, depending on the type of development. Wildlife near cities could enhance culture through inspiring art, poetry etc. Like forests & jungles, or the proposed Natural Wonders, wildlife would also help keep people happy in the late game. With this in mind, it should be possible to establish nature preserves in any wildlife-bearing terrain - not just forest & jungle.