My games have not been peaceful at all. I have not often been the target of attack, but the civ's quite happily ravage each other. Last I night I started a game where Dutch and Assyria were both sending settlers to the exact same spot on the map. William got there first, but less than twenty turns later his city was razed to the ground.
FYI, a sciences panalty has also been applied for each puppeted city. So, there's even elss incentive to capture cities.
However, I would say your statement begs are greater question. You ask "why attack neighboring civ's" I ask "what makes expanding worthwhile at all".
In that selfsame game, I have a spot within easy rich of my capital that has gems. But that's pretty much all it has, so I have to realize it's simply not worth it to settle it. After all, the happiness gain from the lux is negated by the very act of settling there. Those gems are just a recipe for misery. Even the wealth will be offset by all the costs of maintaining the city.
Now, there's a wodnerful spot with horses, iron, cotton, a river, flood plains. a couple wheat, and even a spot by the coast. It would really rock. But I'd need a road no less than six tiles long to connect the two. Is that nice spot worth decrementing my economy with a long road?
