Battle field communications
The ability to ask your allies to flank or wait until ..., or any other simple command.
The ability for your AI allies troops to refuse.
Reduced command ability if your army is too big (see above)
More involved logistics (Some empires have found winter supplies in Russia can be hard to obtain)

Campaign
Not for the TW games, but ones like it. Start as a lower ranking officer/soldier and work your way up to commander of the armies. While you are a lower soldier the AI takes over your empire, when you reach a certain level you are the governor of a city/province, and after another level you get to be the (omnipresent) king until you die. (And restart as another low ranking officer).

mfberg