19 14, the China government proposed to hold a meeting in London to solve the Tibet issue reasonably. At that time, because the British colonial forces had completely controlled the local political power in Tibet, Britain agreed to hold a "meeting on Tibet" and asked the local government in Tibet to send representatives to attend the meeting, and set the meeting place in Simla, India. This is the so-called Sino-British "Simla Conference". At the meeting, Henry McMahon, the British representative, randomly drew a line on the map, allocated a piece of land of about 90,000 square kilometers in China to India, and forced Chen Yifan, the Chinese negotiator, to sign the draft treaty without the consent of the Qing government.

The "McMahon Line" is illegal in law and arbitrary in demarcation principle, so it does not conform to any demarcation principle. The Indian government said afterwards that the "wheat line" conforms to the watershed principle, but the watershed principle is only a principle considered in the demarcation, and the national and cultural principles are more important than the watershed principle. What's more, the "wheat line" cut off the Weihe River system and the Yarlung Zangbo River system; Geographically speaking, the slope from north to south in this area is not big, so it is easy to pass, and it is the only passage connecting China, Xinjiang and Tibet. Further west, it is the towering Karakorum Mountain, which is extremely difficult to pass. So the "wheat line" does not conform to the watershed principle. Even the Indian government did not deny this later.

Because of the illegality of the "wheat line", the makers of this boundary line dare not openly admit its legal existence. The Acheson Treaty Collection published by the British and Indian governments in 1929 admitted that the representative of China did not formally sign the treaty. In the next 20 years, the "Wheat Line" was not marked in the map collection published by The Times, and the Sino-Indian border was still at the southern foot of the Himalayas, which was completely consistent with China's claim.

From 65438 to 0935, the British and Indian governments included the Treaty of Simla in the Acheson Treaty Collection, and mapped the specific location of the "Wheat Line" in The Times Atlas of the World. The fourteenth volume of the new edition of the Acheson Treaty Collection was actually published in 1937, but in order to hide people's eyes and ears, they faked it and passed it off as 1929, and all the original editions were recovered and destroyed. Fortunately, there is still a first edition of the Acheson Treaty Collection in the library of Harvard University, which makes the perjury committed by the British government obvious.

Although the location of the "wheat line" is marked on the map, neither the British nor the Indian authorities dare to regard it as the official border between China and India, but mark it as "undefined". Even the map of Tibet (1938) issued by the Indian Bureau of Surveying and Mapping later indicated that Tawang, south of the "Maixian", belonged to Tibet. Even Nehru's Discovery of India, published in 1946, still shows that India's border lies at the southern foot of the Himalayas.

Because they know in their hearts that this sneaky book is disgraceful and has no legal effect, and they can't deny the objective fact that the Tibetan local government has long exercised administrative power over Tawang. So soon, India arrived in Wangwang for a field trip and collected taxes from local residents. However, when the Indian patrol arrived in Tawang, the local government of Tibet immediately protested to the British side and asked the British personnel to evacuate. Finally, the British colonialists drove away the management agencies of the local authorities in Tibet by force and set up points in Tawang and other places. The concoction of the "wheat line" has actually become another incentive for the Sino-Indian border dispute.