Another important change can be seen from this time on.  Under the feudal system of the Chou strict primogeniture among the nobility existed:  the fief went to the oldest son by the main wife.  The younger sons were given independent pieces of land with its inhabitants as new, secondary fiefs.  With the increase in population there was no more such land that could be set up as a new fief.  From now on, primogeniture was retained in the field of ritual and religion down to the present time:  only the oldest son of the main wife represents the family in the ancestor worship ceremonies; only the oldest son of the emperor could become his successor.  But the landed property from now on was equally divided among all sons.  Occasionally the oldest son was given some extra land to enable him to pay the expenses for the family ancestral worship.  Mobile property, on the other side, was not so strictly regulated and often the oldest son was given preferential treatment in the inheritance.

The technique of cultivation underwent some significant changes.  The animal-drawn plough seems to have been invented during this period, and from now on, some metal agricultural implements like iron sickles and iron plough-shares became more common.  A fallow system was introduced so that cultivation became more intensive.  Manuring of fields was already known in Shang time.  It seems that the consumption of meat decreased from this period on:  less mutton and beef were eaten.  Pig and dog became the main sources of meat, and higher consumption of beans made up for the loss of proteins.  All this indicates a strong population increase.  We have no statistics for this period, but by 400 B.C. it is conceivable that the population under the control of the various individual states comprised something around twenty-five millions.  The eastern plains emerge more and more as centres of production.

The increased use of metal and the invention of coins greatly stimulated trade.  Iron which now became quite common, was produced mainly in Shansi, other metals in South China.  But what were the traders to do with their profits?  Even later in China, and almost down to recent times, it was never possible to hoard large quantities of money.  Normally the money was of copper, and a considerable capital in the form of copper coin took up a good deal of room and was not easy to conceal.  If anyone had much money, everyone in his village knew it.  No one dared to hoard to any extent for fear of attracting bandits and creating lasting insecurity.  On the other hand the merchants wanted to attain the standard of living which the nobles, the landowners, used to have.  Thus they began to invest their money in land.  This was all the easier for them since it often happened that one of the lesser nobles or a peasant fell deeply into debt to a merchant and found himself compelled to give up his land in payment of the debt.