I don't know just how plausible the following scenario is (I apologize in advance if it turns too ASB). But I think it's one of the few remotely plausible ways to turn most of China Jewish.
Most of it was also taken/inspired from a short story by Judith Tarr called "Measureless to Men" from Harry Turtledove's
Alternate Generals III.
POD: c. 1142: The girl who will one day be known as "the Honored Deborah" in Eastern Jewish mythology is born to a family of Jewish merchants in Bukhara, in the Kara-Khanid Khanate.
c.1143-1160: It is thought by modern historians that Deborah somehow receives a detailed instruction on the history and rituals of the Jewish people from a relative, possibly her father. What is known (from records in Chengdu and Karakorum), is that in the year 1160 (by the calendars of Christendom), Deborah is taken by Qarluq slavers while on a journey with her family on the Silk Road and brutally raped in the process, to the point where she was, “left as bereft as the Taklamakan and as vengeful as a winter storm” (to quote the 1227 document
The Secret History of the Mongols). It is speculated by historians in Nanjing and Kaifeng that this is when she swears revenge on the Qarluq.
c.1162: Temujin, the who will one day strike terror into the world around him as Judah, Ghengis Khan, is born to Yesugei, the leader of Kiyad, in Mongolia, and a vassal of Ong Khan of the Kerait tribe, of the Borjigin Clan.
c.1161-1170: Deborah is sold to a plethora of masters, before finally becoming the property of Dei Seichen of the Onggirat tribe in 1170. He also happens to be the father of Borte, the future wife of Temujin.
c. 1170 onwards: For his part, Dei Seichen treats Deborah with indifference when it comes to her religion, allowing her to practice it openly.
One of her main tasks is to look after young Borte. For her part, Borte becomes curious about Deborah’s strange religion. Seeing how Borte is betrothed the son of a local chief, Deborah takes the opportunity to tell her the story of her people and the enduring strength of her people’s Covenant with the Lord God. She tells Borte many stories from the Five Books of Moses during this time as well.
Borte is very intrigued, especially after Deborah tells her how Judaism, despite suffering under tyrannies and great empires ranging from Babylon to Rome, has survived long past their fall.
It’s unknown precisely when Borte declared her conversion to Judaism. Regardless, as various historians have established, she was already practicing her interpretation of the rituals Deborah passed to her by the time of her marriage to Temujin. Records indicate that Deborah had passed away by this time (from an unknown cause).
While all this is going on, Temujin becomes estranged from his tribe and is abandoned with his family to the wilderness, eking out a living on the steppe.
c.1182: Temujin is enslaved by his former tribe; he eventually manages to escape with a sympathetic guard who would later father his general, Chilaun.
c.1188-1200: As previously arranged by his father, Temujin marries Borte. Borte tries to tell him of the power of the “Lord of the Skies and Earth,” but he scoffs at this strange philosophy that she’s apparently trying to teach him. Borte merely tells him that the Lord will lead him to his destiny by any means necessary, as
The Secret History of the Mongols tells us.
Around 1190 Temujin forges a small confederation from his supporters and family of Mongols.
c.1200:
Borte is kidnapped in a raid by the Merkit tribe. In sheer desperation afterwards, Temujin prays to Borte’s “Lord of the Skies and Earth” for his rescue attempt to be successful, and for her to be safe.
With aid from his friend (and future rival) Jamuqa and Ong Khan, along with 20,000 Kerait warriors from his father's blood brother Toghrul, Temujin rescues Borte and destroys the kidnappers. On the way to rescue her, Temujin later tells Borte, he had a fitful dream in which a “Mighty Spirit” told him that his prayer had been successful and his attempt would succeed (though modern day scholars stress that he was under a great deal of duress at the time, and therefore it would be expectant for him to have such a dream; naturally the faithful refuse to even comprehend such a thought).
Borte tells him that it was the Lord God speaking to him. Then, she tells him that she knew all along his attempt would succeed, as the Lord provides for those under his Covenant.
This is all that’s needed to convince Temujin; he declares his conversion to serve the “Lord of the Skies and Earth” until the day he passes on.
Temujin manages to convert Ong Khan to this new religion, along with his brothers—Khaser, Khajiun, and Temuge—his mother Hoelun, his sister Temulin, and his half brothers Bekhter and Belgutei, along with the bulk of the Kerait tribe and the Borjigin Clan. Jamuqa, however, refuses to convert, causing a rift between the two former friends that will never be healed, ending their Blood Brotherhood.
Temujin also moves his followers to convert to his new religion, after ensuring that his tale of the "miracle" spreads far and wide. It’s during this time that the Yassa Code (whose variations govern much of the east to this day) comes into being for the first time. It’s likely that Borte had a heavy hand in their design, as it incorporates what she remembers of the Ten Commandments into the Code.
Borte has by now, according to
The Secret History of the Mongols informed her husband of the existence of the original “People of the Covenant” to the west. Temujin vows to one day find these communities and bring them under his protection.
But first he has to deal with Jamuqa, who has now become Gur Khan (universal ruler) in his own right, a direct challenge to his authority. Combined with his defiance of Temujin’s efforts to spread Judaism, he raises the ire of Temujin.
Although he defeats Temujin in several battles, Jamuqa makes the fatal mistake of encouraging ethnic divisions in his forces, while Temujin uses every opportunity to unify his forces by allowing promotion based on merit and spreading the faith in the Lord of Hosts. Combined with aid from Toghrul--
who unlike IOTL does not side with Jamuqa, as he’s more influenced by Temujin’s new faith even than his own son—it doesn’t take long before Jamuqa is captured and executed by Temujin, having spurned one last offer of forgiveness (and conversion).
1205: By this time, Temujin has brought the formerly various Keraits, Uyghurs, Merkits, Naimans, and Mongols under his control, ensured the diffusion of Judaism amongst them, and having vanquished his rival Jamuqa, declares that he has taken the name new name Judah (after the son of Jacob), and the new title Warrior of the One God. He declares to his soldiers that God has taken them into His Covenant, and that it is the duty, as soldiers of the Lord of Hosts, to conquer the world and bring it into the Covenant. The Mongol Empire is born.
1206-1211: After a brutal series of invasions, the Western Xia Dynasty acknowledges Judah Khan as their overlord. By 1211 the Dynasty’s old lands have been absorbed into the Mongol Empire.
1212-1215: Judah subjugates the Jin Dynasty, concluding with the sack of their capital of Yanjing.
In his wake from the two major conquests, Judah leaves his son Chatagai to implement the Yassa Law in the newly conquered lands. The first mass conversions to Judaism happen during this time. However, Chatagai is forced to crush several revolts as he tries to purge the lands of all pagan influences, which he finds almost impossible. However, he does succeed in establishing the first Houses of the Host in the major urban centers of the former Xia and Jin.
Of course, historians emphasize how chaotic the situation must have been; after all, Judah Khan wasn’t exactly planning to cross the rivers by feeling the stones when it came to religious worship.
Meanwhile, Judah hears that the surviving Jin government has reassembled in Kaifeng, the same city with a strange community of people who came from far away and who believe in one God. Feeling like the Lord of Hosts is leading him on, Judah decides to take his forces to Kaifeng....
~~~~~
Comments? Too ASB? This certainly isn't my greatest area of expertise.