"Qin" in ancient times refers to the Guanzhong and Longyou areas, which is the political center of the Tang Dynasty and the place where the Li family made a fortune. Tang Gaozu named Li Shimin King of Qin, in fact, it was intended to give him the greatest benefit, so that he could operate Guanzhong and Longyou areas with peace of mind and protect the royal family in the Tang Dynasty. The key is the future emperor, Prince Li.

Extended data:

On June 2, 626, near the Xuanwu Gate in Chang 'an Miyagi, the imperial capital, the Crown Prince Li and Yuanji Wang were shot and killed, which is called "the change of Xuanwu Gate" in history.

Later, Li and Li Yuanji were killed and removed from the genealogy. Tang gaozu gave the military and political power to Li Shimin, the king of Qin. Three days later (July 5, June 7, 626), Li Shimin was appointed as the Crown Prince. He wrote: "From now on, all military affairs, big or small, will be carried out by the prince, and then listen to the emperor."

On the 9th Jiazi Day in August of Wude (September 4th, 626), Li Yuan abdicated as the emperor's father, and became the Zen master of Li Shimin. Li Shimin ascended the throne as emperor, and the following year he changed his chastity.

Shiguang in Zhumadian. Com- Why did Li Shimin call Li Shimin the King of Qin and be named the King of Qin?

Baidu Encyclopedia-Li Shimin