When the areas occupied by these chieftains happened to be economically of equal strength, the objective material condition for a sort of balance of power existed, and when other ~actors did not upset the balance, there would be a protracted period of division.During periods of division, which inevitably involved struggle, rival rulers not infrequently resorted to the construction of public works for water-control.This competition in constructive activity, going on simultaneously with the wanton destruction common to feudal wars, generally ended with an upset of the balance and the creation of a new dominant economic area. The events during the last years of the Three Kingdoms, a classical example of division, when the complicating factor of nomadic invasion was absent,offer a noteworthy example. From Huang Ch'u (221-226) to the Tsin dynasty (265-419), able ministers all considered the cutting of canals and storing of grain the means for military preparations."
Whenever such a dominant economic area was in existence, the chieftain who seized control of the Key Economic Area obtained a predominant material advantage over the other contending groups and could eventually put the country under one rule. With unity thus achieved, the ruling group, in order to maintain its power, generally paid special attention to the further development of the agricultural productivity and transport facilities of this Key Economic Area. The study of Chinese history.from the standpoint of the Key Economic Area as a lever of control will therefore throw much light on the central question of unity and division