I think the problem comes in the fact that the game is not structured so that playing to win encourages 'role playing'
The biggest issue with this is the Civ3 UN..it is TOTALLY pointless in a game with Players who are all playing to win.. The point is there should be Some reason for all players to want to merge into a world government (or continental government) ala EU.
The point to be made is that Winning needs to be more than an all or nothing thing. Those countries that join the EU, or states that joined the US, etc. do so because they feel their people will be better for it, that the leaders will be remembered well, etc. and so forth.
By reflecting that in the 'points' that a player gets at the end of the game, or rather accumulates each turn...
ie (the French 'player' gets points each turn even though the French 'civ' no longer exists and the only human player involved (the former Italian 'player') is actually running the EU..that 'player' also doesn't get points for the whole EU but only for Italy's fraction)....
If that happened and AI's were programmed to maximize their ranking (not necessarily to shoot for #1 but to get the best rank they think they can get) then there would be a reason to act 'historically'.
Human players might still shoot for Total Solo Domination, but as that got harder and harder at different difficulty levels, they might go for being Italy joining the EU knowing They won't win (Italy's fraction of EU points being smaller than France's), but that They can a) keep playing as a major power and b) guarantee themselves a top rank when the EU wins the Space Race, which Italy alone could never do.
I feel that with some game based incentive for 'mergers' and more 'civs' (which increases diplomacy, because when there are 100 civs that means that 'public opinion' is worth listening too since a super power probably only controls ~20% of the economy) would make the game more 'historical'
a 'Minor Civ' would be any Civ down on its luck.. the AI algorithms would be the same, but because the input would be drastically different, the behavior would be drastically different. so Persia or Greece would switch from being a 'Minor' to a 'major' civ depending on the circumstances, when Minor the goal is to avoid elimination, when Major the Goal is to get ready to win