I think that the diplomatic section may be the most overlooked part of the game, simply because of the number of wars being fought. Maybe that's because with the AI set to aggressive, it causes the vast number of conflicts.
The diplomat AI is for the most part excellent. I have been stumped sometimes, planning a war against an enemy only to have all hopes scuppered because they have anticpated my move, and countered my alliance.
The only problem is that alliances can tend to be a little static. The AI does move around a bit during peace, but as a human it is possible to keep the same allies for 300 years. Part of this is that it's so risky to allow an ally to drop off in the hopes of getting a new one, as that nation's alliance may extend infinitely. I spent 120 years waiting for England's alliance to expire, they were in bed with Spain, and the Spanish spent all that time going to war with the Incas, Aztecs and North Africans.
Perhaps if a nation is in war alone, then the alliance should not extend, or the 10 years runs from whenever a nation makes peace. That would mean, that rather than every ally coming up for renewal on the same day, the alliance would be in a more constant state of flux.
The long alliances also leads to relatively painless though expensive vassalization and annexation. While the path of peace is commendable, the number of peacefull annexations can be exagerrated. It should be almost impossible to annex another nation. There is simply no rationale for Lorraine to agree to be annexed by France, even if they have been close friends and allies for 200 years. It should take some catastrophic disaster, such as a dynasty dying out, or some economic problems which lead to a country being unable to continue independently (these could be very rare random or historical events)
I would also like to be able to tempt another nation to leave their alliance (not necesarily to come to mine) as this would add to the dipolmatic intrigue, especially if the AI does it to you. For instance Spain might persuade Navarre to switch allegiances, then DOW on France.
While there are a couple of events which improve and worsen relations, it would also be nice if their were some more dramatic events which did even more damage; ruining relations to -200, a nation leaving an alliance, or drasticaly improving relations, just so that there are more dynamic shifts in alliances which would reflect the historical situation.
There was an excellent suggestion on the board a while back for partition events - the opposite of inheritence where your Kingdom might be split up after a monarch's death. I'd love to see that implemented, as well as nations being able to challenge dynastic inheritance. After all, Austria might have a strong case to go to war with France, should that nation inherit Bavaria. These additions might lead to the inheritance wars of history playing out in the campaign game.
Finally, while I have no objection to diplomatic gifts costing me money, there are times when I resent the receiving nation from gaining cash which might be used against me. For example, as France there may be a time when you want to improve relations with Spain enough to get a Royal Marriage to ensure a little peace between the two nations. However, how often is a human player going to give their most dangerous enemy money which may be used against them? Perhaps, a system where gifts cost money, but the receiver doesn't benefit. After all, if I send the King of Lorraine an expensive Persian carpet, or Indian diamond, I would be quite peeved if he sold it off to buy troops. Maybe that method would allow AI nations to make attempts to befriend the human nation without giving them money, as sometimes diplomacy is a bit of a one way street. Making a distinction between gifts and subsidies might expand diplomatic avenues even further.
I doubt any of this would be possible in a patch, but EU2 anyone? I expect it on the shelves by summer please
