Normal: Slight penalty to AI economy
Hard: Small bonuses to AI economy, about 1/2 of the ones on Empire.
Very Hard: Bigger bonuses to AI economy, equal to the bonuses the AI gets on Hard in Empire.
This information is taken from the Shimazu campaign diary. This is my point:
The AI is not ZOMGUNFAIR cheating. They are not behaving like idiots. They play like good, aggressive human players.
The game is not too hard. You are just not good enough to beat it.
I've already beaten the game on normal as Date and am on my way to beating it on hard as Chokosabe. Please, instead of complaining about the game on these forums, play a lower difficulty level until you can gain the skills neccessary to beat it. This game is not like the other horrendously easy TW games. If M2TW was the Sims, this is Dwarf Fortress. You need to adapt instead of blaming your problems on outside influences.