In the earlier wars fought between the nobles they were themselves the actual combatants, accompanied only by their retinue. As the struggles for power grew in severity, each noble hired such mercenaries as he could, for instance the landless nobles just mentioned. Very soon it became the custom to arm peasants and send them to the wars. This substantially increased the armies. The numbers of soldiers who were killed in particular battles may have been greatly exaggerated (in a single battle in 260 B.C., for instance, the number who lost their lives was put at 450,000, a quite impossible figure); but there must have been armies of several thousand men, perhaps as many as 10,000. The population had grown considerably by that time.
The armies of the earlier period consisted mainly of the nobles in their war chariots; each chariot surrounded by the retinue of the nobleman. Now came large troops of commoners as infantry as well, drawn from the peasant population. To these, cavalry were first added in the fifth century B.C., by the northern state of Chao (in the present Shansi), following the example of its Turkish and Mongol neighbours. The general theory among ethnologists is that the horse was first harnessed to a chariot, and that riding came much later; but it is my opinion that riders were known earlier, but could not be efficiently employed in war because the practice had not begun of fighting in disciplined troops of horsemen, and the art had not been learnt of shooting accurately with the bow from the back of a galloping horse, especially shooting to the rear. In any case, its cavalry gave the feudal state of Chao a military advantage for a short time. Soon the other northern states copied it one after another--especially Ch'in, in north-west China. The introduction of cavalry brought a change in clothing all over China, for the former long skirt-like garb could not be worn on horseback. Trousers and the riding-cap were introduced from the north.
The new technique of war made it important for every state to possess as many soldiers as possible, and where it could to reduce the enemy's numbers. One result of this was that wars became much more sanguinary; another was that men in other countries were induced to immigrate and settle as peasants, so that the taxes they paid should provide the means for further recruitment of soldiers. In the state of Ch'in, especially, the practice soon started of using the whole of the peasantry simultaneously as a rough soldiery. Hence that state was particularly anxious to attract peasants in large numbers.