actually there have been several civil wars throughout the empires history. Although the main reason to create them would be territory. The empire has the largest portion of land compared to anyone, it would be better if they were split up to stop them having a huge advantage over other factions.

btw in kingdoms the crusader campaign has set diplomacy maybe you could set it so that they wont declare war (unless the player does it) also you might be able to get it so that its Order vs Chaos