What about lowering your status is it possible. I've just always thought it was 15 provinces = the armies of doom come and that was just a reminder. So back to the question what are the Realm Divide triggers? I was under the impression that only conquering 15 provinces triggered it.
I take 2-3 towns AI takes 2-3 towns and that goes on for 10 years. I do not want to repeat that experience again as its borderline retarded taking over the same 10 cities over and over again. I was battling everyone for about 10 years last time and lost due to timer running out on my short campaign with around 20 something provinces under my belt. Sure I will be able to survive the initial shock wave, entrench and rebuild but last time that happen on legendary the campaign became very frustrating war of attrition.
I would like to avoid such surprises in the future because without an ability to plan for realm divide on legendary there is no way I can beat the campaign.
Some rebels take over one of the provinces I retake it the next turn and get realm divide. I was playing Oda on legendary and finally doing well with about 12-14 provinces fluctuating within my grasp and finally was able to establish peace and began building my bankroll for next expansion push.