They were history's most famous and ferocious warriors. From the Huns to the Mongols, successive waves of nomadic horsemen swept out of the great steppes of Central Asia and wreaked havoc on the static civilizations of Europe, India, and China. How were they so successful? And, what were the limits of their powers? An esteemed professor--who specializes in Arabic and medieval studies--reveals just how "underdeveloped" societies spawned such great generals, from Attila to Genghis Khan; how nomadic Arabs swarmed from the desert in the 7th century to carve out an empire that stretched from Spain to the Chinese frontier; why the Mongols failed to conquer Europe; and where those unique, seaborne raiders, the Vikings, fit into this story.