The rival confederations of the twelfth-century Mongolian plateau — Khamag Mongol, Kereit, Naiman, Merkit and Tatar — herding, raiding and shifting alliances between the fall of the Liao and the rise of Temüjin, who broke and absorbed each of them in turn.
Unified in 1206, when the kurultai at the Onon River proclaimed Temüjin as Genghis Khan — the tribes became the Mongol Empire.
The Mongols' own 13th-century chronicle of the tribal world and Temüjin's rise, in a modern translation.
The standard scholarly biography — the first half is the best account of steppe tribal politics before 1206.