Yeah, the Chinese are sort of the reverse-Borg. "Our resistance is futile. You will be assimilated!"
There's innumerable examples of horse-riding nomads storming in off the steppes, overthrowing the Emperor, and congratulating themselves on having taken over the jewel of the known world. And then realizing that there's 10,000 of them and 100,000,000 Chinese. So they're going to have to learn to speak the language, and hire a bunch of Han to run the bureaucracy, and teach their kids, and...next thing you know, their decadent Chinese-speaking descendants are being overthrown by the next batch of Siberian horselords.
This assimilation effect was so well known that when the Manchu took over, Nurhachi placed his summer capital deep inside Manchuria, and demanded all the nobles and their sons attend him so they could practice horse-riding, archery, speaking Manchu, etc.
It still didn't work.
As far as I know, the only places where the Mongols where actually halted where Japan (because of them damn kamikazes), South-East Asia (because of them damn jungles), and Egypt/Arabia (Because of them damn deserts). I don't think they took India either, but I can't remember the reason.
To some extent, they did...the Timurids were descendants of parts of Genghis's great horde that remained in the areas of Transoxiana that he conquered. They, in turn, evolved into the Mughal Empire which conquered the nothern half of India and most of Pakistan.
To bring this back on topic a bit...in my current game, the Golden Horde converted to Orthodoxy, which was a bit of a surprise. Unfortunately, they were then shattered by the various Russian princes and the Poles. I was kind of looking forward to seeing what havoc an Orthodox horde could wreak. And in the vacuum left by their fall, the Ilkhanate has become the Mighty Scythe of Allah, cutting a swath across the land from the Volga river nearly to Cairo. I'm very curious to see just how far they'll go (and what monstrosity they will become in EU3).
I've managed to weather the storm brought about by Finn the Kinslayer, executing him shortly before my death and leaving the kingdom to his son, Oswiu (later Oswiu the Great), who brought the Lords of Moray to heel, and forged the Triple Crown of the Celts by adding Wales into his fold. It was in his reign that the capital was moved from Ireland, first to Gwent and thence into Cumberland.
Lost my shot at the Norwegian crown, but it was a bad time for it anyways. It was briefly annexed unto the kingdom of Castille, but after two ill-loved Castillian monarchs, a major revolt placed the crown (and most of the Norwegian lands) back under House Staden. I still have a weak claim but it's not worth the effort. My main goal now is to whittle down England enough to forge the Imperial Crown of Brittania. The English throne has been held by the House of Yngling since Harold Hardrade deposed Harold the Confessor (the name England obviously deriving from "Yngling-land")
But England recently came under the sway of a rival upstart Norwegian house, that of Nott. The "rightful" heir, Prince Ivar Yngling, remains Duke of Kent with nearly half the kingdom to his name, but his attempt at a civil war failed, despite the support of most of the lords of the realm and my own interference. It's an elective monarchy, and I hold the county of Durham (as part of Northumberland), so I'm an elector and candidate. Not sure whether to attempt a peaceful HRE-style path of diplomacy and intrigue to ascend the throne by election, or just wait until a moment when they're torn by civil war again and just try to nom up a big honking chunk (either the Midlands, loyal to Prince Ivar; or Somerset/Devon, loyal to the usurper Queen Gertrud).
Gotta say, I have quickly come to LOVE this game.