This is actually a thread in praise of the AI, which I have done in the past.
I was playing on Monarch level as the French, against 4 others on a standard map. England, China and Germany were sharing a continent, and Russia, and I on our own continent. Germany was definately the superpower of the world, with me running a distant second. I managed to avoid any war up into the early 1900's, and was minding my own business, tending to my infastructure (trying to will a cultural or UN victory). I was trading my many resources to keep the other empires happy and was paying little attention to what they were doing. Germany called me up and asked to join a mutal protection agreement. Since we were the world powers, I thought it seemed like a good idea. Wrong. After they got me on board, Germany proceeded to declare war on England, which then brought China to their defense. And then Russia decided it would join in the battle to stop Germany as well. It was a total world war. After about 10 turns Germany had lost much of it's northern border to England and China, and I was producing units non-stop to keep the Russians out of my territory. Germany was clearly losing the war. What a mistake it was to agree to Germany's mutal protection agreement.
The moral of the story is: watch who you agree to defend! I think it's cool how crafty the other civs can be. Germany obviously checked the world standing and thought I'd make a good partner for world conquest. Although, I'll have to admit I stabbed them in the back, made peace with the others and joined in the destruction of Germany. Heh, even got a city with 2 oil resources from them.
Yeah; I get a real kick of the diplomatic relations; they're really unpredictable. Maybe that's just because I haven't played 150 games yet.