Genghis Khan - Khan of All Mongols - Extra History - #4
some details left out in the telling:
Temujin and Ong Khan had actually campaigned against the Naiman around 1199: the Naiman Khan had died and split his realm between his two sons, Tayang and Buiruk who began scheming against each other. Temujin and Ong Khan attacked Tayang, but an army from Buiruk then approached them. According to the Secret History of the Mongols, Jamuhka was present alongside Temujin and Ong Khan (the Secret History of the Mongols sometimes does whatever it wants with the chronology, so we don't know if Jamuhka was actually there or not) and convinced Ong Khan to abandon Temujin in the night. The Naiman army then followed Ong Khan, defeated him and began raiding Kereit territory, and it was up to Temujin to defeat the Naiams and reinstate Ong Khan's control over his own territory.
After Ong Khan had betrayed Temujin, he allied with Jamuhka and they attacked Temujin. At the battle known as Qalqaljit Sands Temujin was defeated and someways, his followers dispersing and with a small band arrived at a Lake Baljuna. Here he made a vow with his followers to lead them to eventual victory, and they all drank from the waters of Baljuna. This became known as the Baljuna Covenant, which was quite famous to the Mongols but interestingly does not appear in the Secret History of the Mongols.
It appears than Temujin's brother Khasar had betrayed him to join Ong Khan and Jamuhka (he wasn't so keen on the upending of steppe traditions possibly), but had had doubts about it and returned to Temujjin, leaving his family behind. To ensure his brother's loyalty, he forced Khasar to kill an envoy of Ong Khan, preventing him from rejoining the Kereit Khan.
It should be noted that there were many other figures involved in the anti-Temujin coalition alongside Jamuhka and Ong Khan, which became problematic as they had different goals in mind, and lacked unity. Temujin used this to his advantage, as he knew this new alliance could not last long. He sent messages to a number of the leaders, reminding some like Ong Khan of past loyalties and issuing threats to others. This helped to disrupt an already shaky coalition, and by the end of the summer there were assassination attempts and betrayals, others deciding that they wanted to take the Kereit throne from the aging Ong Khan for themselves. Thus, by the time Temujin had regained his strength and forces and was ready to counterattack, Ong Khan had been isolated and was vulnerable.
After Ong Khan's defeat the conspirators coalesced around Tayang Khan of the Naiman as noted in the video. However they suffered from disunity. Tayang Khan wanted to draw the Mongol further into Naiman territory in a sort of extended feigned retreat. He was unable to get his brother Buiruk to supply forces for this defence though, and his own wife/step-mother Gurbesu, his son Kuchlug and his leading generals all accused him of cowardice and wanted to attack Temujin head on, which Tayang agreed to reluctantly. According to the Secret History of the Mongols, Jamuhka then spends the early part of the battle frightening Tayang Khan with stories of the invincibility of Temujin's forces (I think he describes Khasar as being able to eat a man whole at one point) and then retreats with his men and leaves Tayang to die. Temujin of course wins and the remaining steppe resistance is slowly destroyed over the following years.
While the Secret History of the Mongols says Temujin gave Jamuhka an bloodless death and says his spirit will look over Temujin's children and descendants, in the history of Rashid al-Din Temujin has Jamuhka slowly cut into pieces and screaming obscenities at him. Take your pick!