You know, this is a hard and tricky subject, cause it is hard to define what "no reason", "neutral", "friendly" exactly mean.
I think there is a problem with AI going into war for a cheap price of a tech, or two. I suggest there should be a certain level of positive relations ratio (+8? +10?) where bribing for war against us (and no other CIV) would be simply impossible. In case of lower ratio, the price should be certainly higher. Other way, there is no sense of relations building.
Interesting that this problem concerns mainly the bribing - friendly AIs don't go for war with us without the encouragement of third side. That comes at least from my experience.
This is relevant to my game and interests.
When I say "Total War"-like AI, I really mean it, as a fanatic Total War game player. The major difference, though, is that the game never tells you when another faction bribes a neutral faction to go to war with you---though you know it's possible because you can actually do that with others.
But the AI in almost all the Total War games (except Empire, which is far more pliable with diplomacy) makes diplomacy pretty much completely useless. About the only thing that can be assured is that neutral factions will agree to trade relations with you.
Everything else is pretty much window dressing---you won't get an alliance out of anyone without some heavy-duty sacrifices on your end, and even then it won't mean jackshit 10 turns later when they decide you have 50 cities, they have 14, you have 7 full-stack armies, they have 2 and a half, and they decide to besiege your capital in London or Rome because declaring war doesn't auto-move hostile forces out of your lands, while your armies are off in Scythia or Morocco, 5 years away.
It's the same situation now in AND1.73 since I don't know when, maybe since 1.71 or so. Diplomacy is pretty much pointless. I know I can almost always get an Embassy and Open Borders established, but beyond that, they're just as likely to go to war with me and suddenly have 2 full-stacked armies on my borders after 1000 years of peace and mutual religious, military, and trade relations as they are to surrender themselves to me as a vassal state.
It's not worth it anymore. Flexible difficulty set me to Immortal difficulty a long-ass time ago and has never returned to lower it.
So I've just gone into World Builder to give myself huge armies just so I can survive without losing half my colonies because 12 of the world's 20 civilizations are at war with me because I took Mansa Munsa as a vassal while he was at war with Bulgaria, who then bribes BUTT
EVERYONE to go to war with me and the only people NOT at war with me are barely city-states themselves, or have peace treaties with me because I just finished ending a brief war with them a few turns ago.
