this is a really cool idea and I would love to see an ancient version of this scenario/stand alone game...

especially without the American connotations..
Couple of ideas.. The 'home' country concept.
1. Would it be possible to keep 'natives' as they are. relatively peaceful clans, tribes etc. that you can trade with and have limited diplomacy with thus representing the smaller peoples.
2. Fellow competing powers are the same relative kingdoms trying to succeed in power etc.. So full diplomacy, trade and war/peace/alliance etc..
3. Trade off screen can be made to foreign powers 'off' the map as such
4. The ' home' powers are replaced by 'a' or 'some' foreign powers who are that big that you must keep them happy as such so they don't come and wipe you out. The same would apply for other competing powers. The idea is to sort of represent Greeks/Persian war... If you beat them back, you win that round and things are quiet again until next time etc...
They could also represent marauding hordes such as the sea people, huns, mongols etc.. They could invade as such against you or one of the other map powers and decide to go on the rampage against everyone etc.. possibilities..
5. Normal victory conditions like map conquest, holding out foreign powers etc..
6. Like Olleus, FF could be techs which would work.
7. In this manner, it doesn't have to be a Greek/Phoenician dominated things
8. The liberty bells could be replaced with 'power' or 'independence' from tribute to these foreign powers above etc..
9. Like Ekmek, Philosophers instead of missionaries. Others could be religious though also.
I like the idea!