There actually aren't any victory conditions for the AIs, and they aren't trying to "win." They're already basically in a sort of stability, mostly at least. It's kind of like feudal Europe, anyhow, in that they each have their kingdoms which are established and they are trying to maintain what they have while also grabbing bits and pieces as they go. They aren't Alexander the Great or Genghis Khan.
This game is really focused on YOU. You're either going to reach that sort of stability in a variety of ways, or you're going to do something more extreme. This game is all about you finding your place in the world, not taking it over (a few side victories notwithstanding). For instance, just because you've diplomatically or economically dominated some other race doesn't mean that that will stay the case in 100 years, for instance. It's like the Saxons and the Franks coming to some sort of mutual agreement/truce for an extended period of time, so that both of their holdings are seemingly secure. But eventually that's going to be disrupted in some way, it's certain.
This game is more about building yourself up from being a powerless nobody -- relatively speaking -- to being an equal player at the very least on the world stage. Possibly you may be what we'd consider a superpower by the time you win, but possibly not.
Odd for a strategy game, no?