The present province of Szechwan, in the west, had belonged to Fu Chien's empire. At the break-up of the Tibetan state that province passed to the southern Chinese empire and gave the southern Chinese access, though it was very difficult access, to the caravan route leading to Turkestan. The small states in Kansu, which dominated the route, now passed on the traffic along two routes, one northward to the Toba and the other alien states in north China, the other through north-west Szechwan to south China. In this way the Kansu states were strengthened both economically and politically, for they were able to direct the commerce either to the northern states or to south China as suited them. When the South Chinese saw the break-up of Fu Chien's empire into numberless fragments, Liu Yue, who was then all-powerful at the South Chinese court, made an attempt to conquer the whole of western China. A great army was sent from South China into the province of Shensi, where the Tibetan empire of the "Later Ch'in" was situated. The Ch'in appealed to the Toba for help, but the Toba were themselves too hotly engaged to be able to spare troops. They also considered that South China would be unable to maintain these conquests, and that they themselves would find them later an easy prey. Thus in 417 the state of "Later Ch'in" received a mortal blow from the South Chinese army. Large numbers of the upper class fled to the Toba. As had been foreseen, the South Chinese were unable to maintain their hold over the conquered territory, and it was annexed with ease by the Hun Ho-lien P'o-p'o. But why not by the Toba?

Towards the end of the fourth century, vestiges of Hun, Hsien-pi, and other tribes had united in Mongolia to form the new people of the Juan-juan (also called Ju-juan or Jou-jan). Scholars disagree as to whether the Juan-juan were Turks or Mongols; European investigators believe them to have been identical with the Avars who appeared in the Near East in 558 and later in Europe, and are inclined, on the strength of a few vestiges of their language, to regard them as Mongols. Investigations concerning the various tribes, however, show that among the Juan-juan there were both Mongol and Turkish tribes, and that the question cannot be decided in favour of either group. Some of the tribes belonging to the Juan-juan had formerly lived in China. Others had lived farther north or west and came into the history of the Far East now for the first time.

This Juan-juan people threatened the Toba in the rear, from the north. It made raids into the Toba empire for the same reasons for which the Huns in the past had raided agrarian China; for agriculture had made considerable progress in the Toba empire. Consequently, before the Toba could attempt to expand southward, the Juan-juan peril must be removed. This was done in the end, after a long series of hard and not always successful struggles. That was why the Toba had played no part in the fighting against South China, and had been unable to take immediate advantage of that fighting.

After 429 the Juan-juan peril no longer existed, and in the years that followed the whole of the small states of the west were destroyed, one after another, by the Toba--the "Hsia kingdom" in 431, bringing down with it the "Western Ch'in", and the "Northern Liang" in 439. The non-Chinese elements of the population of those countries were moved northwards and served the Toba as soldiers; the Chinese also, especially the remains of the Kansu "Western Liang" state (conquered in 420), were enslaved, and some of them transferred to the north. Here again, however, the influence of the Chinese gentry made itself felt after a short time. As we know, the Chinese of "Western Liang" in Kansu had originally migrated there from eastern China. Their eastern relatives who had come under Toba rule through the conquest of eastern China and who through their family connections with Chinese officials of the Toba empire had found safety, brought their influence to bear on behalf of the Chinese of Kansu, so that several families regained office and social standing.

[Illustration: Map 4: The Toba empire _(about A.D. 500)_]

Their expansion into Kansu gave the Toba control of the commerce with Turkestan, and there are many mentions of tribute missions to the Toba court in the years that followed, some even from India. The Toba also spread in the east. And finally there was fighting with South China (430-431), which brought to the Toba empire a large part of the province of Honan with the old capital, Loyang. Thus about 440 the Toba must be described as the most powerful state in the Far East, ruling the whole of North China.