From: Nashville, Tennessee
I've had games where the AI is very peaceful and also where it is aggressive. I think it is reluctant to declare war with you if you have a stronger military. If you've been friendly and aren't weak I think it seems inclined to stay friendly. You can always choose to go attack someone, no need to wait for them :-)
I haven't experienced war like this AI wages since MOO. My tree huggers (-20% combat) have managed to get into a war, now around 50 turns long, with the religious nuts (+20 combat power). I'm holding out, but the game is likely lost due to the lost of tempo to other factions. Not to spoil any surprises, but I'm amazed at how well the AI understands the ins and outs of unit design and operations...
Like MOO, as someone posted above, I'm guessing the setup dictates much of the difficulty and aggressiveness.
Most everyone comments about the SMAC similarities, but I see a lot of MOO here... and for me that's about as good as it gets.
Rex Lex or Lex Rex?