Originally Posted by
Perspective
I would break things down into basic actions, like attacking a unit in neutral territory, invading enemy territory, expanding your territory, etc... As well as the state of the game (I have an alliance, x territory, x units).
All of these can then be fed to a scoring function for a particular goal. If you have a goal to make an alliance, than attacking a unit in neutral territory carries negative weight for that goal. Invading an enemy carries even worse weight. However, they carry positive weight towards other goals such as winning the game. Not having an alliance also contributes negatively to winning the game. etc..
The AI then evaluates the effect of candidate actions on all of it's goals and chooses accordingly. Different AI strategies will value (or weight) goals differently. Tuning these weights (or learning them) is what makes a good AI.