1. Legally speaking, it was established during Shang Yang's political reform, and the government collected taxes according to the number of households; The more separation, the more tax sources, the more tax revenue.

2. Brothers always have to divide, brothers don't divide, cousins also have to divide, and families can't grow up forever;

Moreover, if the family is too big, it will need more pastures, hunting grounds or farms, and it will be farther and farther to go to work, and it will be uneconomical to spend too much time on the road.

Therefore, it is stipulated that men must marry and women must marry (the principle is to be sixteen years old before the nominal age).