Generals developing certain traits as a result of the way you use them. Flag bearers and officers shouting orders on the battlefield. The way your population gets unhappy if you attack a friendly nation but patriotic if you attack a hostile nation.
We’ve put a lot of effort into improving how the player’s behaviour impacts diplomatic relations with different AI nations, and into making the AI behave in an intuitive manner. It’s very important for the player’s sense of immersion in a believable world of rival countries that other nations respond in a way that makes sense in terms of how the player has been behaving. For example if you back-stab your allies, the whole world will see you as dishonourable and you will lose friends quickly. Religious and political differences will all impact how the AI views you, as will your alliances and wars with other nations. In addition, different nations will have different personalities with preferences for different kinds of activity - for example a preference for naval power or for research and building up economically.