I thought this might be a good topic on its own.
1. Early on in the game (until the discovery of Nationalism) you can only get armies if you have a great leader.
2. Armies are much stronger than single units (since they share hitpoints
http://apolyton.net/forums/showthrea...threadid=25180 )
3. Great leader does not last forever (how long is teh question, but I guess Firaxis has play-balanced it well)
Therefore if you get a great leader early, you could be well off to start conquering you neighbours with your army, which would make your empie rise.) However after your great leader dies, you lose this ability, and you cannot conquer easily, if at all, after.
Someone else gets a great leader in the meantime, and than their empire could be growing, and at the expense of yours.
So here you have it... rise and fall of empires.
The only question is if you can get great leaders out of armies?
Armies will presumably fight all the time, and win, and therefore be a great great-leader farm, which would give unfair advantage to the player who gets to the great leader first. If you cannot have great leaders out of armies, than everyone is on pretty much the same foot, and can hope that one of their elite single unit wins will produce a great leader.
I like this idea, but this is only speculation so far.
Any opinions?