When the empire had been unified by the destruction of the feudal states, the central government became responsible for the protection of the frontiers from attack from without. In the south there were only peoples in a very low state of civilization, who could offer no serious menace to the Chinese. The trading colonies that gradually extended to Canton and still farther south served as Chinese administrative centres for provinces and prefectures, with small but adequate armies of their own, so that in case of need they could defend themselves. In the north the position was much more difficult. In addition to their conquest within China, the rulers of Ch'in had pushed their frontier far to the north. The nomad tribes had been pressed back and deprived of their best pasturage, namely the Ordos region. When the livelihood of nomad peoples is affected, when they are threatened with starvation, their tribes often collect round a tribal leader who promises new pasturage and better conditions of life for all who take part in the common campaigns. In this way the first great union of tribes in the north of China came into existence in this period, forming the realm of the Hsiung-nu under their first leader, T'ou-man. This first realm of the Hsiung-nu was not yet extensive, but its ambitious and warlike attitude made it a danger to Ch'in. It was therefore decided to maintain a large permanent army in the north. In addition to this, the frontier walls already existing in the mountains were rebuilt and made into a single great system. Thus came into existence in 214 B.C., out of the blood and sweat of countless pressed labourers, the famous Great Wall. On one of his periodical journeys the emperor fell ill and died. His death was the signal for the rising of many rebellious elements. Nobles rose in order to regain power and influence; generals rose because they objected to the permanent pressure from the central administration and their supervision by controllers; men of the people rose as popular leaders because the people were more tormented than ever by forced labour, generally at a distance from their homes. Within a few months there were six different rebellions and six different "rulers". Assassinations became the order of the day; the young heir to the throne was removed in this way and replaced by another young prince. But as early as 206 B.C. one of the rebels, Liu Chi (also called Liu Pang), entered the capital and dethroned the nominal emperor. Liu Chi at first had to retreat and was involved in hard fighting with a rival, but gradually he succeeded in gaining the upper hand and defeated not only his rival but also the other eighteen states that had been set up anew in China in those years. THE MIDDLE AGES Chapter Six THE HAN DYNASTY (206 B.C.-A.D. 220) I _Development of the gentry-state_