I think by now it's pretty clear what me and many think about the realm divide mechanic. It's asinine both in it's basic idea and it's implementation, and it's nothing more than a cover-up for for an CAI that's still sorely lacking. Ultimately it forces the player to bum-rush to the ending of the game, completely crippling diplomacy and removing the ability to just enjoy a slower growth and advance.
Luckily, not all hope is lost.
According to CA (or more probably, due to an oversight in their coding, since it doesn't make much sense), all the AI factions existing before realm divide takes place are shoguncide maniacs that prefer total annihilation to having a potentially trusted long-time friend on the throne of shogun. All the factions that see the light afterwards (for instance liberated vassals), suddenly decide that they don't want to be shogun, and have their rulers shed their wordly ambition in order to retire to a zen hermitage.
To put it down simply. After Realm divide is issued, it will affect only those factions on the map when it was issued. Any faction emerged afterwards will NOT suffer from it.
So here's how I restored some of the fun and vartety to my Tokugawa campaign after realm divide took effect and completely killed the fun for a few tens of turns.
Initially I decided to turtle, since I had plenty forces to steamroll any enemy that came my way, my allies and previous vassals all slowly betrayed me, and I finally found myself fighting against the world. I was still easily able to fend them off, but it simoply wasn't fun. Diplomacy didn't exist, commerce didn't exist. It was only a long sequence of battles involving always the same armies, and boredom came fast.
Then I took a territory from the uesugi (my longest time allies that just decided to betray me) to secure my eastern border better, and just to try and spice it up a little, i liberated the territory instead of annexing it. That's when I noticed that the new clan was strangely happy and loyal. They had some fairly big "historical grievances" malus (but that was set to become better with time)m but nowhere comparable to the massive realm divide maluses i had.
So I decided to go on a liberation crusade both westwards and eastwards, steamrolling for a few turns whatever traitor clan was in my path and liberating several clans (12 so far). I also noted all the regions that didn't give me an option for liberation and instead of conquering those, I isolated them and used my monks to cause rebellions, then left them behind for my new vassals to conquer and expand (it's safe to leave rebels behind your lines, since they never go on the offensive), given that CA thought that just giving territories to my vassals wasn't "historically accurate" (LOL, LOL, and more LOL ), I have to go at it the roundabout way.
To spice things up a bit, every time I liberate a clan I give them the same "package" proposal.
I give them 1000 koku
Make them join the war against all my enemies
I give them unlimited military access to my lands (ensures that they'll have plenty room to fight)
Commercial agreement
The results are quite interesting.
vassals before the realm divide are quite annoying, as your allies have the very strong habit to declare war on them even when they're not even bordering (I actually believe it's another crap scripted behavior in order to make the ai "appear" more challenging, dragging you into wars against your own allies). This doesn't happen a while after the realm divide, since you do NOT have allies, and even the ones you have are set to betray you anyway, so you may as well get rid of them.
If ALL your allies are vassals, there's no risk, since vassals can declare war only on you, and not on each other, but since they have no reason to hate you (they are not affected by realm divide), you basically get a steel alliance of all the clans you liberate against the clans that betrayed you.
Maybe some of them will declare war on me in the future, but then I'll just have fun by crushing the aggressor and liberating him just again, restoring the status quo
Diplomacy becomes an option again (even if maimed, since it's too stable. Still better than not being an option at all of course), and commerce flourishes anew, as the new clans will not only pay tribute, but will also buy your trade goods. Never had so much income in the whole campaign.
The game finally becomes fun again (even if less than it could be if realm divide wasn't such an asinine mechanic), because you can focus on building and growing while your armies protect your newfound allies against the old traitors (that's needed, since the new clans are obviously small, while the ones that betrayed you are big and bloated), and support them in their mission to slowly erode the power of your enemies. Which is actually a nice change of pace, since you finally get a lot of multi-faction battles, both defensive and offensive.
Some will say it's an exploit of an oversight in coding the realm divide mechanic, and I actually agree. But honestly I don't care, it restores part of the fun that realm divide kills, and I hope those that don't enjoy the mechanic will be able to get a bit more fun out of the endgame thanks to this, like I did.
ad:
Ik heb nog een kleine 10 jaar om tot in kyoto te geraken.
die zich rondom al de andere clans bevinden 
) en koop de andere om met 30k gold om mijn ally te blijven.