Kingdom of Sikkim in the context of "Nathu La and Cho La clashes"

Nanda Devi is the second-highest mountain in India, after Kangchenjunga, and the highest located entirely within the country. (Kangchenjunga is on the border of India and Nepal.) Nanda Devi is the 23rd-highest peak in the world and ranked 74th by prominence in Chamoli Garhwal district of Uttarakhand, in northern India.

Nanda Devi was considered the highest mountain in the world before computations in 1808 proved Dhaulagiri to be higher. It was also the highest mountain in India until 1975, when Sikkim, an independent kingdom until 1948 and a protectorate of India thereafter, became a state of India. It is located in the Chamoli district of Uttarakhand, between the Rishiganga valley on the west and the Goriganga valley on the east.

The Siliguri Corridor, often dubbed the "Chicken's Neck", is a stretch of land around the city of Siliguri in West Bengal, India. 20–22 kilometres (12–14 mi) at the narrowest section, this geopolitical and geoeconomical corridor connects the seven states of northeast India to the rest of India. The countries of Nepal and Bangladesh lie on each side of the corridor and the Kingdom of Bhutan lies at the northern end of the corridor. The Kingdom of Sikkim formerly lay on the northern side of the corridor, until its merger with India in 1975.

The city of Siliguri is the major city in the area and the central transfer point connecting Bhutan, Nepal, Bangladesh, Sikkim, Darjeeling, Northeast India and mainland India. According to the Indian Army, the Siliguri Corridor is the Army's strongest defensive line.

Sikkim (/ˈsɪkɪm/ SIK-im; Nepali: [ˈsikːim]) is a state in northeastern India. It borders Bhutan in the east, the Tibet Autonomous Region of China in the north and northeast, Koshi Province of Nepal in the west, and West Bengal in the south. Sikkim is also close to the Siliguri Corridor, which borders Bangladesh. Sikkim is the least populous and second-smallest among the Indian states. Situated in the Eastern Himalaya, Sikkim is notable for its biodiversity, including alpine and subtropical climates, as well as being a host to Kangchenjunga, the highest peak in India and third-highest on Earth. Sikkim's capital and largest city is Gangtok. Almost 35% of the state is covered by Khangchendzonga National Park – a UNESCO World Heritage Site.

The Kingdom of Sikkim was founded by the Namgyal dynasty in the 17th century. It was ruled by Buddhist priest-kings known as the Chogyal. It became a princely state of the British Indian Empire in 1890. Following Indian independence, Sikkim continued its protectorate status with the Union of India after 1947 and the Republic of India after 1950. It enjoyed the highest literacy rate and per capita income among Himalayan states. In 1973, anti-royalist riots took place in front of the Chogyal's palace. In 1975, after the Indian Army took over the city of Gangtok, a referendum was held that led to the dissolution of the monarchy and Sikkim's joining India as its 22nd state.

East Bengal (/bɛnˈɡɔːl/; Bengali: পূর্ব বাংলা/পূর্ববঙ্গ Purbô Bangla/Purbôbongo) was the easternmost and non-contiguous province of the Dominion of Pakistan, which covered the territory of modern-day Bangladesh. It consisted of the eastern portion of the British administrative Bengal province and the lion half of Sylhet district from the Assam province. East Bengal existed from 1947 until 1956, when it was re-structured as East Pakistan under the One Unit Scheme by the Constitution of Pakistan of 1956. East Bengal had a coastline along the Bay of Bengal to the south, and bordered India to the north, west, and east and shared a small border with Burma (presently known as Myanmar) to the southeast. It was situated near, but did not share a border with Nepal, Tibet, the Kingdom of Bhutan and the Kingdom of Sikkim. Its capital was Dacca, now known as Dhaka.

The Partition of India, which divided Bengal along religious lines, established the borders of the Muslim-majority area of East Bengal. The province existed during the reign of two monarchs, George VI and Elizabeth II; and three governors-general, Muhammad Ali Jinnah, Khawaja Nazimuddin and Ghulam Muhammad. Its provincial governors included a British administrator and several Pakistani statesmen. Its chief ministership was held by leading Bengali politicians.

The Chogyal ("Dharma Kings", Tibetan: ཆོས་རྒྱལ, Wylie: chos rgyal) were the monarchs of the former Kingdom of Sikkim, which belonged to the Namgyal dynasty (Tibetan: རྣམ་རྒྱལ་རྒྱལ་རབས།, Wylie: Rnam Rgyal Rgyal Rabs). The Chogyal was the absolute monarch of Sikkim from 1642 to 1973, and the constitutional monarch from 1973 to 1975, when the monarchy was abolished and the Sikkimese people voted in a referendum to make Sikkim the 22nd state of India.

A referendum on abolishing the monarchy was held in the Kingdom of Sikkim on 14 April 1975. Official results stated the proposal was approved by 97.55% of voters with a turnout of about 63%, and resulted in the country becoming an Indian state.