China’s Cosmopolitan Empire: The Tang Dynasty, by Mark Edward Lewis; Harvard University Press, 2009, 368 pages, US$35. Established after four centuries of division in 618, the Tang dynasty has been regarded by most Chinese as the political and cultural highpoint of imperial China. Between the civil war that led to its founding, the An Lushan rebellion of 756 in the mid-Tang, and the end of the dynasty in 907, China changed in ways that would shape the remainder of Chinese history. In China’s Cosmopolitan Empire: The Tang Dynasty, part of the magisterial six-volume History of Imperial China, Mark Edward Lewis…