I don't know If this general idea hasn't allready been talked about (couldn't find it through a quick search), But I think it would be a good Idea to Have an ambassador units:
Obiously it would come from the consulate, at a rather High level.
I expect we would cost a lot a upkeep and cost about 6 horse (because ambassador don't ride, they travel in coach)(so alliance don't have too many of them, you will understand why later).
When arriving on a town, the unit would be captured and released only if the target player accepts.
Once freed, the ambassador would remain until he is either recalled (by owner), expelled (by target), or killed (by target, or enemie's assassin).
A freed ambassador would give a steady stream of info to the owner, mainly about incoming diplomatique or millitary attaque (as soon as the info incoming hostile appears, the owner of the ambassador would receive a message warning him).
This would allow for big alliance to send reenforcement sooner even if the concerned player is offline.
The large upkeep would prevent overusing of this fonction...
And why not make it compulsory to send an ambassador before being able to invite someone in your alliance? (after the contract has been signed, the ambassador could return home of course)
Thats pretty much all I can think of. Please and your thought to it.
PS; Why not also make the ambassador necessary to go and ask NPC armies to become temporarily your mercenary. It would go with a few caravan filled with gift, and if the gift is not enough all would be destroyed.
Edited by bartimeus - 16 Jul 2010 at 18:06