Brief introduction of Yu Sanjia
Imperial Third Academy (ごさんけ), a social term, comes from the Edo period in Japan. It originally refers to the separation of the three branches (Tokugawa royal family) that have the right to inherit foreign generals except Tokugawa royal family. Later generations refer to three recognized schools in the same field. After Japanese unification, Tokugawa Ieyasu established a shogunate in Edo, which was called the Edo era. Later historians called it Tokugawa shogunate.
In order to consolidate his political power, Tokugawa Ieyasu, like the previous shogunate, divided the names of various places in Japan into three grades according to the close relationship with the Tokugawa family. The closest name is related to the Tokugawa family. He sealed the land near Edo to his relatives and called it the name of pro-vassal.
Among them, Tokugawa Ieyasu's nine men, Tokugawa Yoshinobu, ten men, Tokugawa Laixuan, and eleven men, Tokugawa Laifang, are the closest relatives and are called the three imperial families. If the general has no children, he will choose a suitable object from the "three royal families" and adopt him as an adopted son to inherit the position of the general.