During the Eastern Han and Three Kingdoms periods, Bashu and Hanzhong belonged to Yizhou, one of the thirteen states in the world. However, during the period of Emperor Taizong, Emperor Taizong divided the world into ten roads for better management, and Sichuan Basin (Bashu) belonged to Jiannan Road, which was called "Jiannan Our Mission". Hanzhong area belongs to Shannan Road.
After the Anshi Rebellion in Xuanzong of Tang Dynasty, in order to better control local festivals and further divide them, Jiannan Road was also divided into "Jiannan East Road" (east of Sichuan Basin) and "Jiannan West Road" (west of Sichuan Basin). It is controlled by "I am the ambassador of the sword in the east and the ambassador of the sword in the west" respectively.
Later, Jiannan Dongchuan was referred to as "Dongchuan" and Jiannan Xichuan was referred to as "Xichuan". In the Song Dynasty, Xichuan Road was set up. Since then, the word "surprising" has become a household name.
However, "Dongchuan" and "Xichuan" both refer to the land of Bashu in Sichuan Basin, and there is no Hanshui River Basin where Hanzhong is located.
At the end of Yuan Dynasty and the beginning of Ming Dynasty, Luo Guanzhong was not a special historian and geographer, but a writer, so he misused the names of "Xichuan" and "Dongchuan" which appeared hundreds of years later in The Romance of the Three Kingdoms.
It is irrelevant to use the title of "Xichuan" in the west of Sichuan Basin with Chengdu as the center and "Dongchuan" in the east of Sichuan Basin with Chongqing as the center on the head of Hanshui Basin. This is why the Romance of the Three Kingdoms is now called Dongchuan Xichuan.
In addition, for fear of misunderstanding, I would like to explain the origin of the name "Sichuan" in a unified way. It is well known that there are four major rivers in Sichuan: Minjiang River, Jialing River, Dadu River and Yangtze River, but this statement is actually wrong.
The Song Dynasty was divided into Xia Chuan Road, Xichuan Road and Xixia West Road, Xichuan Road was divided into Yizhou Road and Lizhou Road, and Xixia Road was divided into Zizhou Road and Kuizhou Road. At this point, there were four roads in Sichuan in the Song Dynasty, collectively called "Sichuan Gorge Four Roads" (referred to as Sichuan for short), and the official position of "Sichuan Ambassador" was established here.
After the demise of the Song Dynasty, the Yuan, Ming and Qing dynasties continued to use the name "Sichuan" until today.