Mongolian Steppe (1190 - 1206): Warrior: Scourge of the Steppe is the second book in the Warrior series.
It tells the story of Temujin's rise to power with the aid of Wang Khan of the Kereit. How he systematically destroyed his enemies to create a Mongolian nation under the guise of adding plunder to his wealth until there was no one left to stand against him.
And the brutality of his revenge when he finds those who left him and his family to die on the steppe.