In the seven decades that have passed since the founding of the United Nations, more than 80 former colonies and territories have become independent, a record worth celebrating. In that same period, however, there have been reverses and losses. No story is perhaps as tragic as what happened 40 years ago to the second-last Himalayan Buddhist kingdom, Sikkim.

Only China, not surprisingly given Indian-Chinese tensions in the Himalayan region, tried to bring a charge of colonialism against India to the UN but was rebuffed at every turn.

In 1975, India capped years of political manipulation and destabilization by intelligence operatives with a brutal military intervention to end Sikkim’s independence and make it an Indian state. Now, four decades later, in a new book — “Sikkim: Requiem for a Himalayan Kingdom” — the Scottish author Andrew Duff retells the Sikkimese story, placing it in its Cold War context. It was a time when a paranoid Indian government under Prime Minister Indira Gandhi, newly aligned with the former Soviet Union in a treaty of friendship, saw threats from the West and China everywhere.

Among those imagined threats were two tragic figures: the last king of Sikkim, the Chogyal, Thondup Namgyal, and his American wife, Hope Cooke, who became the focus of Prime Minister Gandhi’s obsession with what she saw as American, specifically Central Intelligence Agency, infiltration. Ironically, the United States did nothing to help the Sikkimese preserve their independence as the situation became more dire and the American government appeared to give tacit backing to India’s version of the takeover.

Cooke, fearing for her life and her childrens’ amid the chaos, fled to New York, where she still lives, immersed in her papers and her memories. With encouragement from her husband, she had thrown herself into the culture and spirit of Sikkim and made numerous efforts to preserve the kingdom’s identity, but that only made matters worse in Gandhi’s suspicious mind. The Chogyal died of cancer in 1982 in a New York hospital, having lost his political fight and something of his will to live.

“His battle was one-sided and against all odds,” wrote B. S. Das, an Indian political officer sent to preside over the end of Sikkimese independence, who never lost his respect for the doomed king. “That did not deter him, as it was a question of his faith in the righteousness of the cause,” Das wrote in a later memoir, “The Sikkim Saga.”

Assessing the loss of Sikkim, Duff said of the last king: “Thondup’s greatest misfortune, of course, had been to find himself dealing with Indira Gandhi, one of India’s most ruthless strategic thinkers, at a time when her concerns about her country’s security were at their height.”

Duff’s book, an enthralling retelling of the Sikkim tragedy, is full of new information drawn from recently released US documents, papers from the period in the British Foreign Office — and, in a remarkably lucky break, the discovery of revealing letters written home by two Scottish women who were headmistresses, successively, of the leading girls’ school in Gangtok, the Sikkimese capital, and knew the royal family.

“I now had first-hand, contemporaneous accounts of the years from 1959 to 1975, during which Thondup and his queen, Hope Cooke, had tried to reinvigorate the Kingdom of Sikkim,” Duff wrote. The human touch of the letters deeply enriches his book, which also benefited from interviews with people in Sikkim, India and the West.

Duff was inspired to start his personal quest to learn about Sikkim from old photograph albums and diary notes of his late grandfather, who had worked in Calcutta in the 1930s and trekked into the Himalayas to discover the little kingdom for himself.

Duff’s book complements and updates the classic first-person history of the fall of Sikkim written by the Calcutta journalist, Sunanda K. Datta-Ray, who became close to the Chogyal as he watched the kingdom disintegrate into violence provoked by hired Indian mobs playing on, or provoking, ethnic divisions between Nepali and Bhutia Sikkimese. (The maneuver has been seared in the collective memory of Bhutan, the last independent Himalayan Buddhist kingdom, now a constitutional monarchy, also with ethnic divisions and fears of India.)

Datta-Ray’s book, “Smash and Grab: Annexation of Sikkim,” first published in 1984 and republished in 2014 as the 40th anniversary of the fall of the kingdom approached, was never officially banned in India, but the author faced charges of defamation and the book was removed from shops. Critics of what they called official Indian disruption and deceit not only in Sikkim but also elsewhere in the region praised the book for its honesty and reliable reporting.

In a recent email interview, Datta-Ray said that he thought that he would never return to Sikkim after the funeral of the last king. But he relented and went back last year at the invitation of the University of Sikkim to deliver an annual academic address.

“I spoke of India’s neighborhood diplomacy, citing Sikkim as an instance of how not to conduct it,” he said. “I dropped in at Gangtok’s main bookshop and found they had just received a large case of the new edition of ‘Smash and Grab.’ “

Like others who have returned to the lost kingdom over the years, he noted how the Indian central government has been pouring development money into the economy, while allowing the Sikkimese to open the only casinos in India — to keep resurgence of nationalism in check.

“The Sikkimese are prosperous as never before.” Datta-Ray wrote in an email. “They get the highest per capita funding from New Delhi. This has always been the central government’s strategy to win over states that are difficult. Money is a great solvent for political grievances.”

Datta-Ray found “little evident nostalgia” for the monarchy in Sikkim last year, but he sensed a noticeable intensifying of a shared Sikkimese culture, which Hope Cooke had once found pervasive during her early years in the kingdom.

“Paradoxically, Indian statehood has brought the majority Nepalese and minority Bhutia-Lepchas closer and created a stronger sense of Sikkimese identity,” he said. He noted that both Nepali and Bhutia people, backed by the state’s Hindu Nepali chief minister, Pawan Kumar Chamling, revere the 17th Karmapa Lama, Ogyen Thinley Dorjee, who escaped from Tibet in 1999 and who, being tutored by the Dalai Lama, is widely respected in Sikkim and among Buddhists in the West.

“Delhi refuses to recognize him,” Datta-Ray said, “fearing he might be a Chinese plant.”

For Datta-Ray, “The most powerful impression today’s Sikkim conveys is one of action, profitable action. Tourism is booming. So are small scale industries. Many of these were planned by the Chogyal but India wouldn’t allow them then. Now India can’t say no. New hotels and guests houses are popping up on the surrounding hills; new shops, bars and restaurants line the pavements. With such a busy present, there’s little time for the past.”

In a recent article in the Business Standard newspaper in India, Datta-Ray suggested that there was no evidential explanation as to why the annexation of Sikkim was a priority for Indira Gandhi. (India already had troops on the border with Tibet and thus China, and the border mountain passes were controlled by the Indian army.) And why, he asked, was the Indian public so easily persuaded to believe the government’s case for overthrowing a monarchy that could do it no real harm to India.

“I am guessing,” Datta-Ray wrote. “What I do know is that India’s media played a disgraceful part. Our newspapers repeated every official lie as gospel truth. And they did so knowingly because they were dazzled by the prospect of expanding borders. Spreading democracy turned territorial acquisitiveness into a moral obligation.

“Will someone in authority please explain why Sikkim had to be acquired and what we have gained by the acquisition?”

Barbara Crossette

Barbara Crossette is the senior consulting editor and writer for PassBlue and the United Nations correspondent for The Nation. She is also a member of the Council on Foreign Relations. She has also contributed to the Oxford Handbook on the United Nations.

Previously, Crossette was the UN bureau chief for The New York Times from 1994 to 2001 and previously its chief correspondent in Southeast Asia and South Asia. She is the author of “So Close to Heaven: The Vanishing Buddhist Kingdoms of the Himalayas,” “The Great Hill Stations of Asia” and a Foreign Policy Association study, “India Changes Course,” in the Foreign Policy Association’s “Great Decisions 2015.”

Crossette won the George Polk award for her coverage in India of the assassination of Rajiv Gandhi in 1991 and the 2010 Shorenstein Prize for her writing on Asia.