I'm sorry for my knowledge of the English language, I use an interpreter.
I want to suggest adding fear to the function of relations between the factions. For example: if the faction of the player, when fighting with any faction, constantly wins, does not suffer losses (do not die, do not lose consciousness), people do not fall into captivity, then the losing faction has fear of the player's faction. Representatives of the losing faction begin to run away from the winners, hide in their buildings and lock the doors. If the faction of the player loses, bears losses, people fall into captivity, then the fear of the faction falls and again accumulates hatred. Also, you can add debuffs to them, for example, to cut the NPS stats. The wars of the losing faction are also exposed to fear, but not all, for example if the fear of the faction is 50 out of 100, then 20% of the guards will also start running and hiding, if the fear of the faction 100 out of 100, then 40% of the guards begin to run away and hide (figures are arbitrary). When the NPS is in a state of fear, it can be robbed. You can also add the opportunity to take tribute from the faction, but then this faction begins to fall into fear and hatred begins to increase.
Thank you for attention. I will be very happy if you like my idea.