Drawing of McMahon line

In 1913–1914 representatives of China, Tibet and Britain met in India ending with the Simla Accord
with Tibetan and British representatives agreeing on the McMahon Line.However, the Chinese representatives refused the territory negotiation. This treaty's objective was to define the borders between Inner and Outer Tibet as well as between Outer Tibet and British India. British administrator, Sir Henry McMahon, drew up the 550 miles 890 km McMahon Line as the border between British India and Outer Tibet during the Simla Conference.

The Tibetan and British representatives at the conference agreed to the line, and Tawang and other areas ceded to the British Empire, since the British were not able to get an acceptance from China, Chinese considered the McMahon line invalid.

The Tibetan and British governments went ahead with the Simla Agreement and declared that the benefits of other articles of this treaty would not be bestowed on China as long as it stays out of the purview.Tibet administered its territory until 1950. The Chinese position was that Tibet was not independent from China: Tibet could not have independently signed treaties, and as per the Anglo-Chinese 1906 and Anglo-Russian 1907 conventions, any such agreement was invalid without Chinese assent.

However, with the collapse of Chinese power in Tibet, the line had no serious challenges as Tibet had signed the convention. In 1935, a Deputy Secretary in the Foreign Department Olaf Caroe "discovered" that McMahon Line was not drawn on official maps. The Survey of India published a map showing the McMahon Line as the official boundary in 1937.

In 1938, the British finally published the Simla Convention as a bilateral accord two decades after the Simla Conference; in 1938 the Survey of India published a detailed map showing Tawang as part of North-East Frontier Agency. In 1944 Britain established administrations in the area from Dirang Dzong in the west to Walong in the east.

The situation developed further as India became independent in 1947 and the People's Republic of China was established in 1949. In November 1950, with the PRC poised to take over Tibet by force, India showed support for the Tibetan government to some extent irking the Chinese government. The McMahon Line was still considered invalid by the new Chinese government.Journalist Sudha Ramachandran argued that China claims Tawang on behalf of Tibetans and Tibetans are not claiming Tawang to be Tibetan territory.

The Dalai Lama was upset over Mao's "Cultural Revolution" which affected Tibet seriously. In January 2007, he said that in 1914 both the Tibetan government and Britain recognized the McMahon Line.In 2008, he said that "Arunchal Pradesh was a part of India under the agreement signed by Tibetan and British representatives".According to the Dalai Lama, "In 1962 during the India-China war, the People's Liberation Army occupied all these areas but they announced a unilateral ceasefire and withdrew, accepting the current international boundary"