[Nick_K]

Diplomacy in the dominions series takes a bit of getting used to...
Basically, the AI will consider itself at peace with you at the start of the game. If you end up at war for any reason it will then attack you quite relentlessly, so all it takes is one battle to trigger a big war.

If the AI attacks you, you attack the AI, you use a non-anonymous province attack spell (e.g. call of the wilds), or (probably) you assasinate a commander of theirs (no 100% about this last one) then you're at war. If you both attack an independant province on the same turn and end up fighting you're not at war. Also, the AI will sometimes attack provinces you're sieging if they're at war with the guys in the fort.

The key is to choose your wars so you don't fight on each front. The way to stop the AI attacking you is to have a strong (especially numerically) force in every border province that they can attack. In the early game I'll build border PD to 20 and try to put a commander or two with troops in each such province to discourage attack. Later you'll need bigger armies and more PD.
This is only really possible if your borders are not large. Try planning your expansion so that you get to bottlenecks and then stop and fortify. Ideally put fortresses in the border provinces so that the AI will be slowed even if they do attack.
Once you have strong borders, choose one enemy - maybe someone you have too large a border with - and attack.
Sending bribes doesn't do anything - I think it's mainly there for multiplayer diplomacy