Genghis Khan and the Making of the Modern World, by Jack Weatherford.
Fascinating book documenting the rise (and inevitable fall) of the Mongol empire. Revisionist, in a nice way. The book is well-documented, and sympathetic to Genghis Khan to a point that is quite surprising, at least for a reader brought up on the standard history books where the Mongols were the wild beasts coming in from the East. Genghis himself comes across as an astute and comparatively open-minded ruler. From the back cover blurb: "Vastly more progressive than his European or Asian counterparts, Genghis Khan abolished torture, granted universal religious freedom, and smashed feudal systems of aristocratic privilege".
It must be said his armies also massacred untold thousands of civilians that had unwisely refused to pay tribute, but that was the norm in those days when you took a city.