There seems to be a little more than meets the eye when it comes to AI-Player relations. I'm currently (Almost done) playing a Huge random map (Multi) against 9 Unfairs, and never once secured an alliance or even a trade partnership with them. The AI seems to react very negatively to aggressive expansion, in the very beginning, all the AI are FFA and will actively blow eachother up, usually however, because we know optimal unit/upgrade combonations, the player takes an empire advantage over the AI. The AI see the human player as a bigger threat, and gang up. What worked for me, is first of all SCOUT. Scout as much as you can as fast as you can, get an idea what the AI is doing. After that, locate your Nearest AI, and try with all your might to take him out as quickly as possible. Sometimes victory hinges on securing the extra resources of that second Terran world. After you feel you've secured enough, bunker down and keep aggression minimal. Turtle up flanks to your Empire. Optimally, you would have just expanded towards the enemy you sought to destroy, making the "rear" of your empire very close to your Capital (at least starting) capital planet. I notice expanding uniformally (IE expanding in more than 1 direction) seems to really piss the AI off, every time I've attempted to secure neutral worlds on both sides of my empire the AI has come down on me with the fury of Thor himself.
The AI assesses threats very differently as well, which can be used to your advantage if you learn what it percieves as threats. Defenses for example, have virtually no impact on a Human player, who will probably go around them or exploit a weakness in a defensive formation. The AI however, assesses the entire planets defenses at once, you could place all your defenses at the ass end of the planet away from any Phase lane and the AI will still avoid that planet with everything but the largest of fleets. Also, unlike most RTS, the AI at least has to Simulate gathering intelligence before it will attack. This is particularly useful on multistar maps. Research as quickly as possible, wormhole or long distance phase jumps, and get to a different star system. Then position Light carriers at the star or wormhole you used to stop enemy scouting parties from locating your planets.
Another point of interest is AI relationships are dynamic as well. A few times I've seen 2 AI allied fleets attacking another AI's planet together, only to have them begin shooting eachother once the colony frigates arrived. If you're patient and are turtled up, eventually the AI will attempt to attack eachother. Even in desperation sometimes, as I lead 2 different fleets on simultaneous strikes on 2 empires, a former ally began attacking a very weak ally to take over their planet.