Speaking of the general trend of the world, if we unite for a long time, we will divide, and if we divide for a long time, we will unite. The same is true for the unification and division of Xinjiang, Mongolia and Tibet with China. Returned to China again and separated after the collapse of the Tang Dynasty; the Yuan Dynasty was the third time; the Qing Dynasty was unified into China for the fourth time so far. Mongolia: Similar to Xinjiang, the Han Dynasty, the Tang Dynasty, the Yuan Dynasty, and the Qing Dynasty have been integrated into the Chinese territory four times so far. Before the Han Dynasty, Qin Shihuang sent Meng Tian to expel the Xiongnu and occupy the Monan (southern Mongolia) prairie, while the Xiongnu fled to Mobei (northern Mongolia). Tibet: Princess Wencheng of the Tang Dynasty made peace with Songtsen Gampo. It is said that the two countries formed an alliance. Yes, you can say that the two countries merged. The first real merger into Chinese territory was the Yuan Dynasty. The Yuan Dynasty established Tibet Province. The emperor of the Yuan Dynasty named the Tibetan monk Phagpa as the national advisor and authorized Phagpa and his successors to manage Tibetan affairs. The Ming Dynasty There are "kings" and "kings of Dharma" to manage Tibetan affairs, and "thousands of households", "village officials" and "inspectors" are arranged to serve in military and political positions in Tibet. The Qing Dynasty adopted the living Buddha system and the ministers stationed in Tibet. The final selection of living Buddhas was issued by the central government of the Qing Dynasty The decision was made by drawing lots from the golden vase, and the minister in charge of Tibet presided over the "enthronement" ceremony on behalf of the central government of the Qing Dynasty. Hence Li Zhaoxing's famous answer to a reporter from Texas, USA: The reporter asked: "Why did you invade Tibet?" , Li Zhaoxing replied: "It has only been two hundred years since Texas was incorporated into the United States, and Tibet has been part of China a thousand years ago. How can you say that your left hand invades your right hand?"