Perhaps I was not concrete enough in my first post.

Ive always played very hard, so I know

a) that the AI on this setting goes to war when you have a common border. I couldnt see from the answers wether it is doing this necessarily on medium. It would already make a big difference if it didnt.

Also I have seen that paying tribute can help very early in the game against factions, which dont have a common border with you, but still tend to go to war , like Greece (naval invasions in Italy, at least with BI-exe). But have anybody experienced this helping later in the game AND with a common border and on what difficulty settings?