China had been an empire for over 1,000 year when the Mongol heir to Genghis, Kublai Khan, roared into the southern part of the country in the 13th century. Carrie Gracie of the BBC has a feature story.
"For the Song (Dynasty), it would been absolutely inconceivable that the Mongols could take over the whole of China," says John Man, author of a biography of Kublai Khan. "It would have been like, I don't know, the Picts taking over the Roman Empire or the Sioux in North America taking over the whole of Canada and the United States - inconceivable. So when it actually happened, the shock was catastrophic."