In the feudal system of the middle ages, the movement of a person from the position of a serf to the position of a landholder was

It was nearly impossible for a serf to become a landholder.

the great wall of china worked as a defense for the feudal states of the zhou dynasty to the north. during the warring states period more walls were put up to defend the borders of the different kingdoms. it was semi successful because despite the wall, the mongols eventually conquered china also the great wall provided protection to the economic development and cultural progress, safeguarded the trading routes such as the silk road, and secured transmission of information and transportation. @jayxboof

would not cooperate with each other voluntarily.