Against them the north had these assets: the possession of the best northern tillage, the control of the trade routes, and "Chinese" culture and administration. At the time, however, these represented only potentialities and not tangible realities. It would have taken ten to twenty years to restore the capacities of the north after its devastation in many wars, to reorganize commerce, and to set up a really reliable administration, and thus to interlock the various elements and consolidate the various tribes. But as early as 383 Fu Chien started his great campaign against the south, with an army of something like a million men. 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 Hsüan, 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 northwards 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.