Retaining good relations with an AI

[Dhampir]

I find it more the opposite. For example, playing the Romans I took Massalia very early and so have a border with the Arverni who are not my allies. Nothing has happened there so far. But my allies the Sweboz dropped a full stack on Mediolanum the very year after we shared border along the Alpes.

I would be tempted to employ my strategic nuclear arsenal.

[jhhowell]

In my experience, having a massive military rating (on the faction rankings graph) probably has the most effect. After seeing the "have a border = declaration of war" behavior of the AI on VH campaign difficulty in my 0.8 Rome campaign, I've mostly played on M to try to avoid that. Yet under 1.0, I played a M Hayasdan campaign and still got jumped by both AS and Pontus in particularly stupid ways (both were allied with me and involved in other wars). Whereas I played around with a VH AS campaign and nobody lifted a finger against me (except the Ptolemies, with the starting war continuing as long as I played that campaign). Military strength is the only explanation I can think of for that behavior, though I'm still a bit surprised Bactria left me alone.

Experience with another mod also circumstantially supports the military rating hypothesis, for what that's worth. So I'd say just go out and keep your army as big as your economy can support - which you probably want to do anyway for other reasons.

[craziii]

make sure your military rating is equal or higher than the AI, when that is maintained, just park 1 full stack in one of the border cities. the AI will not attack unless it's sure it has advantage.