Chinese soldiers guarding the border at the Nathula mountain pass connecting India and China’s Tibet Autonomous Region in 1967. In September 1967, deadly border clashes broke out at Nathula between India and China, after India installed barbed wire barriers along the ridges of Nathula, partly encroaching on Chinese-controlled territory.
The view toward the Border Control Inspection Building at the Nathula Pass from the Indian side of the border. In September 2014, a year after the old pilgrim’s way through the Lipulekh Pass was badly damaged by flooding, Indian External Affairs Minister Sushma Swaraj and her Chinese counterpart Wang Yi signed a memorandum of understanding on opening a new route for Indian pilgrims to undertake the Kailash-Manasarovar Yatra.
1642: Sikkim, earlier known as Bayul Dremojong (literally means “hidden valley of rice”), came in existence as a hereditary monarchy in the Eastern Himalayas in the mid-17th century. It was considerably larger than it is these days. Sikkim frontiers included part of eastern Nepal, northern Bengal, western Bhutan, and southern Tibet.
1788: The Chumbi/Dromo Valley that projects southward from the Tibetan Plateau, intervening between Sikkim and Bhutan via the mountain passes of Nathu La and Jelep La, had long been a strategic location for trans-Himalayan trade and military operations. In the hope of taking control of a formal trade route established in 1784 through the Chumbi Valley, Nepal invaded Sikkim in 1788 and further advanced into southern Tibet.
1792: Sikkim became a protectorate of Qing China after the Sino-Nepalese War (1788–1792), one of the Qianlong Emperor’s Ten Great Campaigns. The Qing Empire stationed a governor at Shashima in the Dromo region, also known by its Chinese name Yadong, and Chumbi Valley was annexed by Tibet.
1817: The British in India wanted to establish trade ties with Tibet on their northern frontier as a way to keep Russian interest at bay, and Sikkim was conceived as a perfect corridor given its close kinship links and religious affiliation with Tibet. After the end of the Anglo-Nepalese War (1814–1816), Sikkim and British India signed the Treaty of Titalia (1817), which enabled the British to take control of Sikkim’s internal and external affairs.
1839: Qing authority over Tibet weakened gradually in the latter half of the 19th century, given the weight of Qing’s domestic and foreign relation burdens, particularly, the Opium War (1839–1842 and 1856–1860) and the Taiping Civil War (1850–1864).
1861: Sikkim and British India signed the Treaty of Tumlong, which secured protection for travelers to Sikkim and guaranteed free trade, making the state a de facto British protectorate. Topographical and geographical surveys of Sikkim were conducted after 1861 to open trade routes and build roads between India and Tibet.
1876: Britain and Qing China signed the Chefoo Convention, known in Chinese as the Yantai Treaty, which specified the extraterritorial privileges of British subjects in China, including the right to open up traffic between India and Tibet.
1890: Britain and Qing China signed the Convention of Calcutta or the Anglo-Chinese Convention of 1890, which was recognized a British protectorate over Sikkim and demarcated the Sikkim–Tibet border.
1893: A protocol was added to the 1890 convention, and the market at Yadong/Dromo was opened to India.
1906: Britain and Qing China signed the Convention Between Great Britain and China Respecting Tibet or the Anglo-Chinese Convention of 1906, and a British trade agent was stationed at Yadong/Dromo.
1911: After Qing was overthrown during the 1911 Chinese Revolution, Tibet became a de facto independent state before the 1951 annexation by the People’s Republic of China. Yadong/Dromo region was controlled by the British.
1947: Following the independence of India, Sikkim continued its protectorate status with the Union of India after 1947 and the Republic of India after 1950.
1954: Agreement on Trade and Intercourse between the Tibet Region of China and India was signed, and China regained control over the Yadong/Dromo region.
1962: Some skirmishes took place at the Nathula Pass during the 1962 Sino-Indian Border War, and border trade was interrupted.
1967: A series of border clashes happened between India and China at Nathula and Cho La alongside the border of Sikkim, then an Indian protectorate.
1975: Sikkim became a state of India.
2003: China and India reached a settlement of their border disputes. India emphasized that Tibet is part of China, and China recognized Sikkim as part of India.
2006: The Sino-Indian trade across the Sino-Indian border at Nathula Pass was revived. The Xining to Lhasa section of the Qinghai–Tibet Railway came into service, and three lines extending from Lhasa have been proposed, including a Lhasa-Shigatse-Yadong Railway.
2015: China opened the second land crossing in Tibet via Nathula to allow Indian pilgrims undertaking the Kailash-Manasarovar Yatra. The old route via Lipulekh Pass was heavily damaged in the floods in 2013.