China, as we all know, is a country with an ancient civilisation. In the valley of the Yangtze Kiang a civilisation which is recognisably Chinese had developed nearly 2,000 years before Christ; about the time when the first bronze-using people were invading Britain, and a thousand years or so before the Greeks sacked Troy, though quite late in the history of the Pharaohs of Egypt. China is a large country, about 1,200 miles by 800, with one great advantage and one disadvantage. The advantage is that the great river-basins are extremely fertile and can support a large population. The disadvantage is that the country has no natural frontier on the north and west. It is easy for the nomadic tribes of central Asia to invade the fertile Chinese plains, and China has many times seen foreign conquerors overthrow the native rulers and set up new dynasties.