Campaign Difficulty :

- Relations between nations vary significantly. On Medium difficulty, relations with factions you are not allied or at war with will shift towards neutral ("don't know 'em, don't care about 'em"), while on Easy they shift towards Perfect, and on Hard/Very Hard they shift towards Abysmal, sharply so in the case of VH.
Since relations affect AI decisions somewhat, this means that while on Easy you'll mostly be left alone, on VH you'll most likely be attacked by everyone.

- Agent efficiency varies. On Medium, your agents (that is, priests + merchants + diplos + princesses + spies + assassins) and enemy agents have the exact same chances. On Easy, your guys are better than those of the AI. On H and VH, your guys have significant penalties to their success rates, and I believe on VH enemy agents also have bonuses against you, which can be a pain in the case of Inquisitors for instance.

- AI factions may or may not have a cash boost on H and VH. I heard both claims, and while I haven't seen anything about it in the game's .txt files, it's possible.


Battlemap difficulty :
- Morale and Fatigue are progressively more important to the player, depending on diff setting. On Easy you can pretty much run your guys all over the place, in the snow, uphill both ways, all the while being charged in the back by Darth Vader, and your boys won't falter nor wheeze. On VH, you have the same morale and fatigue values the computer has.

- Cleverer AI : it's been said that the AI makes less mistakes on VH, handles it's forces better etc..., but I'm inclined to believe it's not the case. The battlefield AI is in a moddable .xml file, and there's precious little about difficulty in it (in fact, the only variable that changes based on difficulty is called "retreat-analyser". May dictate at which time the computer will throw in the towel I suppose ?)

- No effect on stats. The AI soldiers are not wargods on VH, nor are they wimps on Easy - your guys and his are equivalent no matter the difficulty.

Did I miss something, TW gurus ?