The humbling of the Song, the Turkification of the Islamic world, the Afghan expansion into northern India, the Crusades—these dramas loom large in the world historical narratives of China, India, the Islamic world, and Europe. From the panoramic point of view, however, they look like a single interwoven drama that began in northern Europe, rippled through the Asian steppes, created disruptions in the urban civilizations along the whole perimeter of that region,
