I've played a few 1v1 and small FFA games against easy AIs and am now engaged in a 3 star, 8 opponent match against normal AIs. I started out as the TEC in the middle star system with 2 Vasari opponents. Another star system has another Vasari opponent. And the third star system contains three Advent and one TEC opponent. I was instantly at war with my closest Vasari neighbor and I did my best to please the races outside of my star system.
Long story short, I eventually made peace with my Vasari neighbor and ganged up on the other one. I took his worlds and then turned my attention to the Vasari who was the lone force in his own star system. He was claiming worlds in our system so I took those. And then, much to the delight of the other AIs, I backstabbed my former-enemy-turned-friend-back-to-enemy Vasari neighbor. Over the course of all of this I had made peace with all three Advent opponents. I was at 100%, 100%, and 83%. The TEC and had got into little scraps that kept us from being friendly.
Then, all of the sudden, two Advent buddies of mine declared war on me (one 100% and the 83%) and our diplomacy dropped to 0%. They dropped all alliances. They both offered me missions soon after and I gave one of them 4000 metal (as the mission requested). All of the sudden they were back at 100% (but without the Cease Fire and Peace niceties).
What happened? Did the AI realize that I am becoming the big dog and turn on me? Or did my heavy use of my two Novaliths in the extermination of my neighboring Vasari have something to do with it? I haven't read anything like this happening against computer opponents. I mean, I'll roll up the sleeves and kick their psychic butts now, but I was just curious.