Primary sources by the Mongols are few, although there are volumes of anecdotal stories from across the width and breadth of Eurasia. Peter Jackson has done a marvelous job of pulling together these scant materials and writing a first-rate history of the Mongols after Chingiss (d. 1227). As the title indicates, Jackson is primarily concerned with the political relations between the "west" (this includes not only the Christendom of the Byzantine Empire and western Europe, but also the Mamelukes and Abbasids in the Near East), although some attention is paid to the commerical relations that emerged under the Mongols.
The foundation of the book rests on Mongol society, and the perception and misconceptions of the "west" around exactly what this was, and how those in power sought to initally resist and (failing that) manipulate the horsemen from the steppe. Essentially the Mongols sought to make the world theirs, eventually failing because of a lack of pasture and from internal strife and conflict among the ruling khans. That said, the Mongols demonstrated a remarkable ability to manipulate and play on the perceptions of Christians and Muslims. To the Christians, the Mongols were at first the wrath of God (mind you, this was the high middle ages), later, when news of Mongol tolerance towards Christianity (and of all other religions, per their policy) reached Rome, efforts were made to enlist them as allies against the Muslims, likewise the Mamelukes (and others) against competing caliphs in the Near East.
I had anticipated a closer study of the Mongols themselves rather than the political relations between the Yuan dynasty, the Il-Khanids, and the White and Golden Hordes relative to the "civilized" west - instead, Jackson only whetted my appetite for more. Still, it is a remarkable treatise on medieval politics and a keen lesson on how one's weltanschauung shapes one's understanding of others. Recommended for the specialist in medieval history.