When one of the sides is dominant, events are triggered at certain intervals. These events are related to whether or not you appease the angered side. If you don't appease the angered side, these periodic events will get worse over time and eventually you will get an event that will drag your country into civil war. Therefore, to prevent this from happening, you will either not make one side dominant or you will choose to calm the angry side in triggered events. If there is a civil war in your country even though the sides are not dominant, then you need to tell us exactly what you are doing and the current situation of the country so that we can fix this bug.