But in the first decade of the twentieth century, as the Manchu dynasty ended, Chinese policy changed sharply in Tibet. Military presence was extended through central Tibet, and more modern institutions replaced the theocratic and ancient machinery of administration, which reducing the role of the Dalai Lama and the power of the monastic orders. By 1910, China had established effective power in Tibet, and the buffer for India to keep Russia away was lost, as the Morning Post in London wrote: "A great Empire, the future military strength of which no man can foresee, has suddenly appeared on the North-East Frontier of India." The British was concerned that China would pose a strategic threat to India, and the forward school recommended more active patrolling in the hills beyond the frontier. It was decided that if China attacked India, Britain would attack China from the sea. The Chief of the General Staff warned of the dangerous pressure through Tawang Tract, and recommended bringing not only Tawang but also a sizeable slice of Tibet into India. From 1911, the Indian government embarked on a deliberate advance of the northeastern boundary. In order not to invite a vigorous Chinese protest, the Indian military made secrete expeditions into the Tibetan tribal belts of Assam which British took for India twenty years ago, bypassing the Parliaments permission. Although it was outside of the external frontiers, the official British maps showed it as part of the frontier. The officials fobbed that "it is not intended to increase the area administered by" the Indian government. The statement was literally true since the Inner Line was not changed, but it was the Outer Line that was advanced.
In 1911-12, the Chinese power in Tibet suddenly collapsed. The British decided that it was in their strategic and political interest to exclude effective Chinese power from Tibet. In 1913, British convoked a conference at Simla which was aimed at making Tibet a buffer state between Britain and China, like the buffer effect to keep the Russians away. McMahon, the Foreign Secretary of the Indian government, led the British delegation to attend the Simla Conference. The British made open effort to make China accept a division of Tibet into Inner and Outer Tibet, as the agreement made by China and Russia in the case of Mongolia. China would have suzerainty over the whole of Tibet, but would have no administrative rights in Outer Tibet, thereby keeping back from the borders of India. The coercive diplomatic methods of Britain brought the weak and unwilling China to the conference. The Chinese representatives stressed the paramount importance of Tibet and resisted its zonal division, keenly aware of the British effort to separate Tibet or at least a great part of it from China. In April 1914, McMahon induced the Chinese official, Ivan Chen, to initiate a draft treaty, but the Chinese government repudiated the unauthorized compliance immediately. McMahon presented the draft to the British, which plainly cancelled its validity. In July, the conference was closed without Chinese signing the convention. London had instructed McMahon all along not to sign bilaterally with Tibetans if China refused, but McMahon proceeded to sign with the Tibetan representative while Ivan Chen was sent to the next room. Chen was not told of what was being signed and the declaration was kept as secret for many years. Although all this provided much fertile ground for international lawyers, the results of the conference were clear, and was accepted as such by the British Government at the time: the Simla Conference produced no agreement to which the government of China was a party. McMahon admitted this himself: "It is with great regret that I leave India without have secured the formal adherence of the Chinese Government to a Tripartite Agreement." China had emphatically and repeatedly denied that Tibet enjoyed sovereign identity and that China would not recognize any bilateral agreement between Tibet and Britain.
A covert byproduct of the Simla Conference was the McMahon Line. It came as a result of the secret discussions, without the Chinese participation or knowledge, which took place in Delhi between the British and the Tibetans in February and March of 1914. These meetings breached not only the Anglo-Chinese Convention of 1906, in which Britain was to "engage not to annex Tibetan territory," but also of the Anglo-Russian Convention of 1907, in which Britain was to engage "not to enter into negotiations with Tibet except through the intermediary of the Chinese Government." The British moved the line progressively to the north of Tawang, which was still short of the goal proposed by the Chief of the General Staff to annex some two thousand square miles of Tibetan territory. McMahon Line essentially pushed the boundary northward about sixty miles, and moved it from the foothills to the crest line of the Assam Himalayas. In doing so, McMahon accomplished for British India what other officials attempted twenty years ago on the Afghan frontier, and brought the tribal no-man land under nominal British sovereignty. China forcefully repudiated the convention and denied the validity of the map, and the Tibetans in practice ignored the Line. In 1919, the British tried once more to induce China to resume the tripartite negotiations. After China refused, the British began providing military aid to Tibetans, including arms, ammunitions, and training in their use. When the British relinquished the Indian Empire in 1947, they started to translate the McMahon Line from the maps as the effective northwest boundary of India, despite that the Line appeared on its maps only ten years before. As the British departed, the new Indian government assured that they would complete their work: "If anything, they intended to pursue an even more forward policy than had the British."
Indias China War by Neville Maxwell