When it comes to alliances, it seems like the AI tends to stick together and pushes the human aside. I once had a bounty of 15,000+ because all the AI players had apparently allied together. Then I started getting missions to kill units from each factions, but I couldn't because they'd amassed all their ships on the two planets next to the only remaining one I had. I'd jump units in, and by the time I'd told them to jump out they'd be dead. I didn't even get a chance to attack with them.