Historically, Tibet was not part of China (there was anyway nothing like China, but Dynasties with boundaries).
Upon the death of Langdarma, the last emperor of a unified Tibetan empire, there was a controversy over whether he would be succeeded by his alleged heir Yumtän or by another son (or nephew) Ösung (either 843-905 or 847-885). A civil war ensued, which effectively ended centralized Tibetan administration until the Sa-skya period. Ösung's allies managed to keep control of Lhasa, and Yumtän was forced to go to Yalung, where he established a separate line of kings. In 910 the tombs of the emperors were defiled.
The son of Ösung was Pälkhortsän (either 893-923 or 865-895). The latter apparently maintained control over much of central Tibet for a time, and sired two sons, Trashi Tsentsän and Thrikhyiding, also called Kyide Nyigön in some sources. Thrikhyiding emigrated to the western Tibetan region of upper Ngari and married a woman of high central Tibetan nobility, with whom he founded a local dynasty.
After the breakup of the Tibetan empire in 842, Nyima-Gon, a representative of the ancient Tibetan royal house, founded the first Ladakh dynasty. Nyima-Gon's kingdom had its center well to the east of present-day Ladakh. Kyide Nyigön's eldest son became ruler of the Mar-yul (Ladakh) region, and his two younger sons ruled western Tibet, founding the Kingdom of Guge and Pu-hrang. At a later period the king of Guge's eldest son, Kor-re, also called Jangchub Yeshe Ö (Byang Chub Ye shes' Od), became a Buddhist monk. He sent young scholars to Kashmir for training and was responsible for inviting Atiśa to Tibet in 1040, thus ushering in the Chidar (Phyi dar) phase of Buddhism in Tibet. The younger son, Srong-nge, administered day to day governmental affairs; it was his sons who carried on the royal line.
Central rule was largely nonexistent over the Tibetan region from 842 to 1247, yet Buddhism had survived surreptitiously in the region of Kham. During the reign of Langdarma three monks had escaped from the troubled region of Lhasa to the region of Mt. Dantig in Amdo. Their disciple Muzu Saelbar (Mu-zu gSal-'bar), later known as the scholar Gongpa Rabsal (Dgongs-pa rab-gsal) (832-915), was responsible for the renewal of Buddhism in northeastern Tibet, and is counted as the progenitor of the Nyingma (Rnying ma pa) school of Tibetan Buddhism. Meanwhile, according to tradition, one of Ösung's descendants, who had an estate near Samye, sent ten young men to be trained by Gongpa Rabsal. Among the ten was Lume Sherab Tshulthrim (Klu-mes Shes-rab Tshul-khrims) (950-1015). Once trained, these young men were ordained to go back into the central Tibetan regions of U and Tsang. The young scholars were able to link up with Atiśa shortly after 1042 and advance the spread and organization of Buddhism in Lho-kha. In that region, the faith eventually coalesced again, with the foundation of the Sakya Monastery in 1073. Over the next two centuries, the Sakya monastery grew to a position of prominence in Tibetan life and culture. The Tsurphu Monastery, home of the Karmapa school of Buddhism, was founded in 1155.
The first documented contact between the Tibetans and the Mongols occurred when Genghis Khan met Tsangpa Dunkhurwa (Gtsang pa Dung khur ba) and six of his disciples, probably in the Tangut empire, in 1215.
After the death of Genghis Khan in 1227, the Tibetans stopped sending tribute to the Mongol Empire. As a result, in 1240, the grandson of Genghis Khan and second son of Ögedei Khan, Prince Godan (or Köden), invaded Tibet. Prince Godan asked his commanders to search for an outstanding Buddhist lama and, as Sakya Pandita, the leader of the Sakya school of Tibetan Buddhism, was considered the most religious, Godan sent him gifts and a letter of "invitation" to come to his capital and formally surrender Tibet to the Mongols. Sakya Pandita arrived in Kokonor in 1246. Prince Godan received various initiation rites and the Sakya sect of Tibetan Buddhism became the religion of the ruling line of Mongol khans. In return, after a third Mongol invasion in 1247 led to the submission of almost all Tibetan states, Sakya Pandita was appointed Viceroy of Tibet by the Mongol court in 1249, marking one of the occasions on which the Chinese base their claim to the rule of Tibet.
The Indian position is based on its traditional opposition to separatist movements and to foreign intervention in support of such movements.
The Tibet issue is rooted in the histories of the three countries – India, China and Tibet. Tibet has existed throughout history as a distinct civilization with rich culture, language, religion, polity and identity. Through the centuries India and Tibet have maintained strong religious and trade ties, and have shared a peaceful border. But the advent of British power in the Indian sub-continent altered the nature of this relationship.
The British policy was shaped by the Great Game that was to prevent Russian expansion to the South.
Independent India inherited the British Agreement which in essence meant that Tibet was a buffer zone and de facto an independent country with Chinese suzerainty. Though India tried to dissuade China from aggression into Tibet, China invaded Tibet.
Nehru during his 1954 visit to China raised the issue of incorrect map, which Chou en Lai took pains to explain that they were old KMT maps, which PRC did not have time to revise.
On December 14, 1958 letter, Nehru in a letter to the PRC govt once again raised the issue of Chinese maps depicting the border alignment inaccurately. This time the Chinese gave a different response. Chou en Lai wrote back on January 23, 1959 stating that the Sino-Indian border was never delimited and that China has never recognised the McMahon Line.
Consequent to the 1962 India-China war, China began to claim some 90,000 square kilometres of Indian Territory in the eastern sector and 38,000 square kilometres in the Aksai Chin area. These claims flow directly from China's control over Tibet and China's internal apprehension over Tibet wherein they had started consolidate its rule over this rebellious territory.
Between 1947 and 1954, India's position on Tibet was based on recognising it as an independent nation. Tibet represented itself as an independent country at the Asian Relations Conference held in New Delhi in March-April 1947. But India subsequently gave up this position on April 29, 1954, when it signed an agreement with China on trade and intercourse between India and Tibet. Under the terms of the agreement, India gave up all extra-territorial rights and privileges that it had inherited from the British Raj and recognised Tibet as part of China. This, in effect, was a unilateral concession without the Indian government gaining anything in return.
