Harold Lamb 
The March of the Barbarians 

An account of four generations of Mongol leaders, from Genghis Khan, through his sons, grandsons, and great-grandsons. The book is arranged into a series of narratives, which are grouped dynastically and chronologically covering the span of the Thirteenth Century, and dealing with the process by which the Mongols came to dominate Central Asia and spread outwards to come into contact with Europe, the Indian sub-continent, and China.