"I don't know Civ4's AI routines, but it might be such that after a certain year passes, it decides that the only way to stop the human player is total war. Bef

"I don't know Civ4's AI routines, but it might be such that after a certain year passes, it decides that the only way to stop the human player is total war. Before that it can be less aggressive." What seems more likely, at least in my experience, is that the AI is always trying to pursue a single goal: beating everyone else. It will select whatever means it deems possible at any point in time. It will make calculations, each turn, about the relative strength of its military versus the strength of its intended target, or else the combined strength of its allies' militaries against the strength of an opposing alliance's militaries. That's about it. It's always looking for an excuse to attack somebody. The only thing that holds it back is any sort of power imbalance sufficiently not in its favor. There are some AI "personalities" and leader traits in the game that will favor more aggressive styles than others. But generally speaking, a more aggressive AI personality is simply an AI personality that has a lower threshold for declaring war. It will go to war with slightly riskier odds than a less aggressive personality will. But they'll all go to total war if the odds are sufficiently stacked in their favor. The "aggressive" trait is really just a sliding scale of risk tolerance.