thumb|The western portion of the McMahon line drawn on Map 1, that was shared by the British and the Tibetan delegates at the Simla Conference, 1914
thumb|The eastern portion of the McMahon line drawn on Map 2, that was shared by the British and the Tibetan delegates at the Simla Conference, 1914
thumb|Henry McMahon
thumb|The McMahon Line forms the basis of the [[Line of Actual Control and the northern boundary of Arunachal Pradesh (shown in red) in the eastern Himalayas administered by India but claimed by China. The area was the eastern sector of the 1962 Sino-Indian War.]]
The McMahon Line is the boundary between Tibet and British India as agreed in the maps and notes exchanged by the respective plenipotentiaries on 24–25 March 1914 at Delhi, as part of the 1914 Simla Convention.
The line delimited the respective spheres of influence of the two countries in the eastern Himalayan region along northeast India and northern Burma (Myanmar), which were earlier undefined.
The Republic of China was not a party to the McMahon Line agreement,
but the line was part of the overall boundary of Tibet defined in the Simla Convention, initialled by all three parties and later repudiated by the government of China.
The Indian part of the Line currently serves as the de facto boundary between China and India, although its legal status is disputed by the People's Republic of China. The Burmese part of the Line was renegotiated by the People's Republic of China and Myanmar.
The line is named after Henry McMahon, foreign secretary of British India and the chief British negotiator of the conference at Simla. The bilateral agreement between Tibet and Britain was signed by McMahon on behalf of the British government and Lonchen Shatra on behalf of the Tibetan government.
It spans from the corner of Bhutan to the Isu Razi Pass on the Burma border, largely along the crest of the Himalayas.
The outcomes of the Simla Conference remained ambiguous for several decades because China did not sign the overall Convention but the British were hopeful of persuading the Chinese. The Convention and the McMahon's agreement were omitted in the 1928 edition of Aitchison's Treaties. It was revived in 1935 by Olaf Caroe, then deputy foreign secretary of British India, who obtained London's permission to implement it as well as to publish a revised version of Aitchison's 1928 Treaties. Since then the McMahon Line has been part of the legal national border of India.
China rejects the Simla Convention and the McMahon Line, contending that Tibet was not a sovereign state and therefore did not have the power to conclude treaties. However China recognizes the line as part of the Line of Actual Control between the two countries, according to a 1959 diplomatic note by Prime Minister Zhou Enlai. Chinese forces briefly occupied a part of this area during the Sino-Indian War of 1962 and later withdrew.
The 14th Dalai Lama did not originally recognise India's sovereignty over Arunachal Pradesh. As late as 2003, he said that "Arunachal Pradesh was actually part of Tibet".
Background
thumb|right|Map of the British Indian Empire from the [[Imperial Gazetteer of India, 1909 showing the Outer Line as the border of Assam.]]
thumb|right|1907 map of East Bengal and Assam from the Imperial Gazetteer of India showing the Outer Line as the border
British India expanded east of Bhutan in the early 19th century with the First Anglo-Burmese War. At the end of the war, the Brahmaputra valley of Assam came under its control, and over the next few decades, under its direct administration. The thickly forested hill tracts surrounding the valley, constituting the present-day Arunachal Pradesh, were inhabited by tribal people, who were not easily amenable to British administrative control. The British were content to leave them alone. In 1873, the British drew an "Inner Line" as an administrative line between the directly-administered territory and the tribal territory, and British subjects were prohibited from passing into the latter without explicit permission.
The British boundary, also called the "Outer Line", was defined to mark the limits of British jurisdiction. But it was not significantly different from the Inner Line in this region.
The British wanted peaceful relations with the Himalayan tribes who lived beyond the Inner Line. However, British influence was nevertheless extended to many regions, through treaties, trade relations, and occasional punitive expeditions in response to "outrages" committed against British civilians.
There is evidence that the British regarded the Assam Himalayan region as a geographical part of India irrespective of political jurisdiction.
Forward policies of early 1900s
By 1900, Chinese influence over Tibet had significantly weakened and the British became apprehensive that Tibet would fall into a Russian orbit. In an effort to preclude Russian influence over Tibet and to enforce their treaty rights, the British launched an expedition to Tibet in 1904, which resulted in the Convention of Lhasa between Tibet and Britain.
Qing China became apprehensive about British inroads into Tibet and responded with its own forward policy. They took complete control over the southeastern Kham region of Tibet (also referred to as the "March Country"), through which passed the Chinese communications to Tibet. An assistant amban (imperial resident) was appointed for Chamdo in western Kham to implement the new strategy. Over a period of three years, 1908–1911, the amban Zhao Erfeng implemented brutal policies of subjugation and sinification in the Kham region, for which he earned the nickname of "Zhao the butcher".
Zhao Erfeng's campaigns entered the Tibetan districts adjoining the Assam Himalayan region such as Zayul, Pomed (Bome County) and Pemako (Medog County). They also encroached into parts of the adjoining tribal territory and attempted to exert influence. This alarmed British officials in the region, who advocated the extension of British jurisdiction into tribal territory.
The higher administration of British India was initially reluctant to concede these demands,
The British appear to have been clear that they were only extending the political administration of their rule but not the geographical extent of India, which was taken to include the Assam Himalayan region.
Tawang tract
Drawing the line
In 1913, British officials met in Simla, to discuss the status of Tibet. The conference was attended by representatives of Britain, China, and Tibet. Suzerainty is an Asian political concept indicating limited authority over a dependent state. The final 3 July 1914 accord lacked any textual boundary delimitations or descriptions. It made reference to a small scale map with very little detail, one that primarily showed lines separating China from "Inner Tibet" and "Inner Tibet" from "Outer Tibet". This map lacked any initials or signatures from the Chinese plenipotentiary Ivan Chen.
Both drafts of this small scale map extend the identical red line symbol between "Inner Tibet" and China further to the southwest, approximating the entire route of the McMahon Line, thus dead ending near Tawang at the Bhutan tripoint. However, neither draft labels "British India" or anything similar in the area that now constitutes Arunachal Pradesh.
The far more detailed McMahon Line map of 24–25 March 1914 was signed only by the Tibetan and British representatives. This map and the McMahon Line negotiations were both without Chinese participation. After Beijing repudiated Simla, the British and Tibetan delegates attached a note denying China any privileges under the agreement and signed it as a bilateral accord. British records show that the Tibetan government accepted the new border on condition that China accept the Simla Convention. As Britain did not to get an acceptance from China, Tibetans considered the McMahon line invalid. The Anglo-Russian Convention was jointly renounced by Russia and Britain in 1921, but the McMahon Line was forgotten until 1935, when interest was revived by civil service officer Olaf Caroe. The Survey of India published a map showing the McMahon Line as the official boundary in 1937. In 1938, the British published the Simla Accord in Aitchison's Treaties. The replacement volume has a false 1929 publication date.
In Beijing, the Communist Party came to power in 1949 and declared its intention to liberate Tibet. India objected at first, but eventually acquiesced to Chinese claims over Tibet and recognised China as the suzerain power. In 1954, India renamed the disputed area the North East Frontier Agency (NEFA).
India acknowledged that Tibet was a part of China and gave up its extraterritorial rights in Tibet inherited from the British in a treaty concluded in April 1954. In the NEFA sector, the new maps gave the hill crest as the boundary, although in some places this line is slightly north of the McMahon Line. Nehru, seeking to quickly assert sovereignty in response, established "as many military posts along the frontier as possible", unannounced and against the advice of his staff. locate Longju a kilometre or two on the China side of the McMahon Line "near the Chinese garrison town of Migyitun" (which is now quite sizeable, at 28°39'40" N latitude, over four kilometres north of the line). (The rarely reliable coordinates in the Geonames database (National Geospatial-Intelligence Agency) incorrectly place "Longju" in snow and ice 10 kilometres away from the river at over 12,000 feet in elevation.) In a letter to Nehru dated 24 October 1959, Zhou Enlai proposed that India and China each withdraw their forces 20 kilometres from the line of actual control (LAC). Shortly afterwards, Zhou defined this line as "the so-called McMahon Line in the east and the line up to which each side exercises actual control in the west". The Soviet Union, United States, and United Kingdom pledged military aid to India. China then withdrew to the McMahon Line and repatriated the Indian prisoners of war (1963). The legacy of the border remains significant especially in India where the government sought to explain its defeat by blaming it on being caught by surprise.
NEFA was renamed Arunachal Pradesh in 1972—Chinese maps refer to the area as South Tibet. In 1981, Chinese leader Deng Xiaoping offered India a "package settlement" of the border issue. Eight rounds of talks followed, but there was no agreement.
In 1984, India Intelligence Bureau personnel in the Tawang region set up an observation post in the Sumdorong Chu Valley just south of the highest hill crest, but three kilometres north of the McMahon Line (the straight-line portion extending east from Bhutan for 30 miles). The IB left the area before winter. In 1986, China deployed troops in the valley before an Indian team arrived. This information created a national uproar when it was revealed to the Indian public. In October 1986, Deng threatened to "teach India a lesson". The Indian Army airlifted a task force to the valley. But the Indians moved three Divisions around Wangdung to face off the Chinese troops at Sumdurung Chu, and stood their ground firmly. The confrontation was defused in May 1987 though, as clearly visible on Google Earth, though recent construction of roads and facilities are visible. The Chinese withdrew in 1995 after 8 long years of talks.
The Indian Prime Minister Rajiv Gandhi visited China in 1988 and agreed to a joint working group on boundary issues which has made little apparent positive progress. A 1993 Sino-Indian agreement set up a group to define the LAC; this group has likewise made no progress. A 1996 Sino-Indian agreement set up "confidence-building measures" to avoid border clashes. Although there have been frequent incidents where one state has charged the other with incursions, causing tense encounters along the McMahon Line following India's nuclear test in 1998 and continuing to the present, both sides generally attribute these to disagreements of less than a kilometre as to the exact location of the LAC.