. At first the advance went well. The horsemen from the
north, however, were men of the mountain country, and in the soggy
plains of the Yangtze region, cut up by hundreds of water-courses and
canals, they suffered from climatic and natural conditions to which they
were unaccustomed. Their main strength was still in cavalry; and they
came to grief. The supplies and reinforcements for the vast army failed
to arrive in time; units did not reach the appointed places at the
appointed dates. The southern troops under the supreme command of Hsieh
Hsuean, far inferior in numbers and militarily of no great efficiency,
made surprise attacks on isolated units before these were in regular
formation. Some they defeated, others they bribed; they spread false
reports. Fu Chien's army was seized with widespread panic, so that he
was compelled to retreat in haste. As he did so it became evident that
his empire had no inner stability: in a very short time it fell into
fragments. The south Chinese had played no direct part in this, for in
spite of their victory they were not strong enough to advance far to the
north.

3 _The fragmentation of north China_

The first to fall away from the Tibetan ruler was a noble of the
Mu-jung, a member of the ruling family of the "Earlier Yen dynasty", who
withdrew during the actual fighting to pursue a policy of his own. With
the vestiges of the Hsien-pi who followed him, mostly cavalry, he fought
his way northward into the old homeland of the Hsien-pi and there, in
central Hopei, founded the "Later Yen dynasty" (384-409), himself
reigning for twelve years. In the remaining thirteen years of the
existence of that dynasty there were no fewer than five rulers, the
last of them a member of another family. The history of this Hsien-pi
dynasty, as of its predecessor, is an unedifying succession of
intrigues; no serious effort was made to build up a true state.

In the same year 384 there was founded, under several other Mu-jung
princes of the ruling family of the "Earlier Yen dynasty", the "Western
Yen dynasty" (384-394). Its nucleus was nothing more than a detachment
of troops of the Hsien-pi which had been thrown by Fu Chien into the
west of his empire, in Shensi, in the neighbourhood of the old capital
Ch'ang-an. There its commanders, on learning the news of Fu Chien's
collapse, declared their independence. In western China, however, far
removed from all liaison with the main body of the Hsien-pi, they