To this date, I've never seen a dominating AI faction... Unlike in MTW, where especially the Almohads/Spanish, English/French and Byzantines/Egyptians always created big armies and empires which created a real challenge to fight, none of the factions in RTW do the same, not even the Romans...They rarely get beyond 10 provinces, which means that they're not really a threat to you.

Are there any way to change the AI to make that happen? For example making them more aggressive, not only against you, but the other AI empires too?

Oh, and also change the priority of training units....I'm sick and tired of facing Armenian and Parthian armies completely made up of Eastern Infantry!