The 'Whole Mongol' union of the Onon-Kherlen grasslands: the first Mongol khanate proper, whose elected khans raided the Jurchen Jin hard enough to buy peace in 1147, and whose collapse under Jin-Tatar blows set the stage for Temujin's reunification. Chinggis Khan's own great-grandfather Qabul was its first khan.
Absorbed into the Mongol Empire at the 1206 quriltai on the Onon, where Temujin — having rebuilt the shattered union — was proclaimed Chinggis Khan.
The 'Mongol tribe' entry is the clearest account of the first Mongol khanate, its khans, its Jin wars and its collapse.
Allsen's narrative of 1196-1206 shows how the fragmented Mongol clans were reassembled into the empire proclaimed at the 1206 quriltai.