This would allow a more realistic determinant for how nations form, are destabilized, conquered and get reborn. It never made sense to me that the game should end when you are conquered. History is full of examples of peoples who have been conquered, only to regain their independence.

I had an idea that you could "design" your group at the start, by applying a set amount of characteristic points to a number of different factors. You may have to decide between things like inventiveness, cultural cohesiveness, work ethic, patriotism, spirituality and stability. These factors would effect things like advancement rate, military unit strength, productivity, effectiveness of different government types, and how your people get along with other peoples (e.g., do your people assimilate quickly with other cultures?)

The most likely route to regaining independence would come from revolts, or as part of a peace settlement between warring nations. That is, a nation that sues for peace may offer to grant cities with majority alien populations their independence (or rather to rejoin their parent country if still present in the game).

By the way, under this plan you would exert the same limitted control over any part of your population, whether you currently have an independent nation or not. In other words, say you have a country, but an enemy takes one of your cities. You would still have this limitted control over your ethnic group in the conquered city. If you attack that power elsewhere, and he decides to sue for peace, he may offer cities that have a large population of your people, such as the one he managed to conquer.

One route to conquest would be to have a population boom, followed by resettling some of your population in neighboring foreign cities, where they could effectively act as spies, saboteurs and potentially fall into your hands after generations, as a result of peace settlements.

I envision a game where populations of various ethnicities have to be managed, and where you don't have absolute control over certain things such as immigration and emigration (unless you decide to forcibly expel aliens, with diplomatic ramifications). Spontaneous migration of peoples, ethnic-based revolts, spontaneous granting of independence and forced resettlement/genocide would add an unprecedented realism. At some point in the game, as for example after the discovery of Age of Reason, harsh treatment of ethnic groups could have serious consequences to your foreign relations.

The differences might be almost imperceptible in the ancient and medieval world, but could become absolutely critical for someone hoping to be a modern military superpower. It would be possible to increase your access to materials by trade, but you might be at the mercy of nations that have monopolies on certain materials. You could also stockpile strategic materials if you mine or buy more than you require currently.