The centralized dynasties that ruled ancient China were a product of the terrain and climate of the Asian continent. China is isolated from the rest of the Eastern hemisphere by formidable natural barriers of mountains on the west and southwest as well as the Gobi Desert on the north. To the east lies the Pacific Ocean. Although China’s separation was not total–trade goods, people and ideas moved back and forth between China, India, and Central Asia–in many respects its development was distinctive.

[question]In its formative years, Chinese civilization had been influenced by the contributing factors of the Yellow River region – the land of the loess. It is generally understood that the river running through a vast area, where the fine and porous soil accounts for the large silt content in its current, has a constant tendency to clog its own course and cause dikes to break and enormous inundations to occur. The problem cannot be dealt with locally.[question] This predicament has a historical origin that can be traced at least to the Spring and Autumn period (722–481 B.C.), when in 652 B.C., Duke Huan of Qi convened his league of states.[question] A mutual pledge by all participants is recorded in various sources as "not to execute improper dikes and not to hinder the water flow." [question]The stone inscriptions of his own achievements erected by the first emperor of the Qin dynasty (221–207 B.C.) are reproduced in The Records of History. [question]One of the meritorious deeds that he credited to himself was the neutralization of the barriers that obstructed water flows. These and other references are evidence that China’s political unification, achieved in the B.C. era had come under the pressing demand for a coordinated effort in dealing with the flood problem which over and above technical considerations has remained in force for the past 2,000 years.

[question]A second factor compelling China to proceed to an early national unification and to follow it with political centralization was the effect of monsoon rain on agriculture. The summer monsoon in China comes from the direction of the Philippine Sea. It by itself does not give rain. The moisture in the air current depends upon winds flowing from west to east and northeast, lifting it to an altitude to be cooled, only then does rain come down from condensation. This climatic arrangement subjects agricultural drops of the nation to the synchronization of two sets of variables. When the two kinds of currents miss each other, drought sets in. When they repeatedly converge over a specific area, flood and inundation are the inevitable result. It is not uncommon for lack of rain and too much rain simultaneously to victimize two or more parts of China. Only an enormous empire in control of vast resources can deal with the situation. The requirement imposed by the power of nature was felt too, during the B.C. era. In one ancient text we read many stories about wars between the principalities during times of natural disaster. The scholar Yao Shanyu, working from ancient summaries, calls attention to the fact that in the 2,117 years under study, 1,621 floods and 1,392 droughts caused damage serious enough to be reported by the imperial courts.

[question][question]Further ruling out the possibility of a decentralized China was the potential threat of nomads. The traditional line of defense that China erected in the north along the steppe–a vast grass-covered plain–customarily referred to as the Great Wall was by no means fixed. The territories north and west of the Great Wall, having an annual rainfall of less than fifteen inches and therefore inadequate for cultivation, remained a grazing ground for the nomads. In times of bad weather and in periods of China’s dynasty, these nomads had a tendency to execute large-scale invasion. This was a problem whose cause was so deeply rooted in geography that the Chinese were not able to solve it merely through military offensives. Long-term experience taught them to put the regional and local government under a strong leader, allowing national defense to dictate a degree of homogeneity and uniformity in order to survive.