In the north, proto-Mongol Hsien-pi tribes had again made themselves independent; in the past they had been subjects of Liu Yuean and then of Shih Lo. A man belonging to one of these tribes, the tribe of the Mu-jung, became the leader of a league of tribes, and in 337 founded the state of Yen. This proto-Mongol state of the Mu-jung, which the historians call the “Earlier Yen” state, conquered parts of southern Manchuria and also the state of Kao-li in Korea, and there began then an immigration of Hsien-pi into Korea, which became noticeable at a later date. The conquest of Korea, which was still, as in the past, a Japanese market and was very wealthy, enormously strengthened the state of Yen. Not until a little later, when Japan’s trade relations were diverted to central China, did Korea’s importance begin to diminish. Although this “Earlier Yen dynasty” of the Mu-jung officially entered on the heritage of the Huns, and its regime was therefore dated only from 352 (until 370), it failed either to subjugate the whole realm of the “Later Chao” or effectively to strengthen the state it had acquired. This old Hun territory had suffered economically from the anti-agrarian nomad tendency of the last of the Hun emperors; and unremunerative wars against the Chinese in the south had done nothing to improve its position. In addition to this, the realm of the Toba was dangerously gaining strength on the flank of the new empire. But the most dangerous enemy was in the west, on former Hun soil, in the province of Shensi—Tibetans, who finally came forward once more with claims to dominance. These were Tibetans of the P’u family, which later changed its name to Fu. The head of the family had worked his way up as a leader of Tibetan auxiliaries under the “Later Chao”, gaining more and more power and following. When under that dynasty the death of Shih Hu marked the beginning of general dissolution, he gathered his Tibetans around him in the west, declared himself independent of the Huns, and made himself emperor of the “Earlier Ch’in dynasty” (351-394). He died in 355, and was followed after a short interregnum by Fu Chien (357-385), who was unquestionably one of the most important figures of the fourth century. This Tibetan empire ultimately defeated the “Earlier Yen dynasty” and annexed the realm of the Mu-jung. Thus the Mu-jung Hsien-pi came under the dominion of the Tibetans; they were distributed among a number of places as garrisons of mounted troops.
The empire of the Tibetans was organized quite differently from the empires of the Huns and the Hsien-pi tribes. The Tibetan organization was purely military and had nothing to do with tribal structure. This had its advantages, for the leader of such a formation had no need to take account of tribal chieftains; he was answerable to no one and possessed considerable personal power. Nor was there any need for him to be of noble rank or descended from an old family. The Tibetan ruler Fu Chien organized all his troops, including the non-Tibetans, on this system, without regard to tribal membership.