The hardy races from the North, which overran the country and kept a Tartar on the Chinese throne for centuries, are virile and pertinacious. It has been the fate of every civilization we know anything about to be wiped out by hardy races.  Rome went down before the Northmen, and England had its oversea conqueror.  Greece and Italy succumbed to the might of brawny arms, and civilization shrank back for hundreds of years.  So China fell before the men of the mountains, and her records were destroyed.