A Civil Wars mechanic is definitely needed to bring this game's mechanics together.
* There's no point in having heirs and dynasties if you can conquer the whole map in a lifetime and have no enemies left to fight. Civil wars would provide an endless source of enemies even after you've "won", and would give us endless replayability in a single save if we wanted it.
* Warband had a simple civil wars mechanic. Obviously good features should be carried over from older games when making a sequel.
* When it comes to faction balance, which has long been a problem for Taleworlds, civil wars would fix the problem. If some factions became overpowered, a civil war could split them in half to balance things out.
Here is my suggestion for how civil wars could work. A rating can be used to influence the likelihood of civil wars occurring, similar to how settlements have loyalty/security ratings. Each faction has a "Unity" percentage rating, which determines the likelihood of it falling into a civil war. When the rating reaches 0%, a civil war occurs and all clans that dislike the leader will rebel. The following things influence likelihood of a civil war.
* If the faction is already at war, Unity rating cannot drop below 0%. This represents the feeling of a common enemy/greater threat. It also serves to prevent civil wars from being too common, or diplomacy getting too confusing.
* Faction wins a war: +10% Unity.
* Faction loses a war: -10% Unity.
* Each new fief gained at the end of a war: -5% Unity. This is an anti-snowballing mechanic which makes empires become less stable if they expand too rapidly.
* New vassal clan joins a faction: -1% Unity.
* Each culture in the territory owned by the faction, that season: -2% Unity. (This can add up to -12%). This means that large, multi-cultural empires suffer from strife within their borders, which makes a civil war gradually more and more likely to occur in a big faction.
* Each clan (in the faction) with +1 to +50 relations with the ruler, that season: +1% Unity.
* Each clan with +51 to +100 relations with the ruler, that season: +2% Unity.
* Each clan with -1 to -50 relations with the ruler, that season: -1% Unity.
* Each clan with -51 to -100 relations with the ruler, that season: -2% Unity.
* Each clan leader in the faction with upstanding trait, that season: +1% Unity.
* Each clan leader in the faction with devious trait, that season: -1% Unity.
* Each clan member with less Influence than the ruler, that season: +1% Unity.
* Each clan member with more Influence than the ruler, that season: -1% Unity.
* If the player succeeds a faction's "expose a plot" quest, it gains 5% Unity.
* If the player succeeds a faction's "plot to depose the monarch" quest, it loses 20% Unity.
* Rebellion occurs: -10% Unity.
* Ruling clan dies entirely: -90% Unity.
* Civil War occurs: Both the new and old faction are set to 100% Unity (Everyone who chose to stay with the ruler is loyal to their choice).
So, for example, let's say that Battania had 10% Unity in the winter of 1090. Caladog is well liked by the majority of Battanian clans (+11%), but is less influential than 5 clans (-5%). Battania controls towns of Sturgian, Vlandian, Empire, and Battanian cultures (so -8% Unity this month due to internal strife). This brings the Unity rating down to a precarious 8%. Then, in the spring of 1091, Caladog is still well liked (+11%), and still holds towns of 4 different cultures (-8%), but has increased his influence to be more influential than three clans (+3%), so the Battanian faction sits at 14% Unity. If Caladog failed to increase his Influence in that year, or died, or lost a war, or had a rebellion occur, Battania would soon fall into civil war.
So for a very small faction with a well-liked, influential leader, civil war is almost impossible. For a very large faction with a disliked and non-influential leader, civil war is bound to happen soon. A default faction with a lord who is neither loved nor hated and has majority influence will take quite some time to have a civil war, which will probably only occur rarely in peacetime.
When a faction's Unity finally drops below 1%, it kicks off a civil war. A new faction is created out of the faction's lords who have the lowest relations with the ruler, or are more influential, or have traitorous/greedy traits. This new faction automatically goes to war with the faction it was created from, and the most influential clan within the new faction becomes its leader and gives the new faction its name and culture: For example, if the Banu Sarran is the most popular clan in the new faction that breaks away from the Aserai, then the new faction will be called the Sarranid Sultanate and have the Aserai culture. In this way, even if a certain culture has its affiliated faction totally wiped out, it can be reborn as a new faction later.
Civil wars should be unlikely for the player to face in their early kingdom. But by the time the player has conquered most of the map, chances should be very high. So there can be two ways to counter civil wars. 1: Travel around your empire doing quests and trying to keep everyone happy. 2: Build up your military strength instead so you can be ready to kill the separatists when the civil war does happen. The player can deal with civil wars at the endgame depending on the play-style they prefer.