Well-field system was a state-owned land system in ancient China, which was recorded in the Shang Dynasty and prevailed in the Western Zhou Dynasty. At that time, roads and passages crisscrossed, dividing the land into "well"-shaped squares, so it was called "ore field". The mining field belongs to the king of Zhou and is distributed to the people. The Lord can not buy or sell, not transfer the mine field, but also pay a certain tribute. The Lord forced the people to collectively cultivate the mine field, surrounded by private fields and in the middle by public fields. Its essence is private ownership of land. (In the Xia, Shang and Western Zhou Dynasties, all the land belonged to the state)

A was chosen because, with the development of productive forces, the strength of vassals became greater, and they no longer obeyed the control of the central authorities, leading to separatism.