The cause was pneumonia, said his wife, Elizabeth Conquest.
Born in England to an American father and a British mother, Conquest was a communist during his student days at the University of Oxford in the late 1930s, but he quickly grew disenchanted with the ideology. After embarking on an initial career as a poet, he would become known on both sides of the Atlantic as one of the West's most important historians of its Cold War nemesis.
In a body of work that spanned a score of books and thousands of pages, Conquest sought — by most accounts, with harrowing success — to document the history of the Soviet Union and particularly the crimes of Joseph Stalin, who led the Communist state from the early 1920s until his death in 1953.
By the time of Conquest's writings, Stalin's crimes were widely known. Even Soviet leader Nikita Khrushchev had denounced him in 1956. But, perhaps more than any other historian, Conquest was credited with documenting those transgressions in painstaking detail. Conquest's account, 20 million people died during the repression and deprivations of Stalin's rule.
Christopher Hitchens — another English-born intellectual and writer who spent much of his life in the United States — called Conquest "the dragon slayer of the Stalinoid apologists" and "the softest voice that ever brought down an ideological tyranny."
Conquest was best known for "The Great Terror," which documented the torture, show trials and wanton murders of supposed "enemies of the people" that Stalin used to quash dissent in the 1930s. The book's publication, in 1968, coincided with the Soviet invasion of Czechoslovakia to end the period of liberalization known as the Prague Spring.
"We must hope that a great many people will glance at this record," George Kennan, the historian and former U.S. ambassador to the Soviet Union, wrote in a New York Times review of the book. "Without some idea of these things, no accurate measure can be taken of the history of our own century, no adequate idea can be formed of the capabilities of modern man for beastliness, no adequate understanding can be gained of the history of the Soviet regime or even the mentality of the present leaders."
After the fall of the Berlin Wall, Conquest offered a revised version of the book in "The Great Terror: A Reassessment" (1990). With the passage of time, the findings of his original volume were largely vindicated.
Conquest also received acclaim for "The Harvest of Sorrow" (1986), about the collectivization of peasant farms under Stalin and the resulting mass starvation that Conquest described as the "terror-famine."
"Fifty years ago as I write these words, the Ukraine and the Ukrainian, Cossack and other areas to the east — a great stretch of territory with some 40 million inhabitants — was like one vast Belsen," he wrote, referring to the Nazi concentration camp in Germany. "In the actions here recorded about 20 human lives were lost for, not every word, but every letter, in the book."
His scholarly achievements were made more notable because he was persona non grata in the Soviet Union and did not set foot there between 1937 and 1989, when it collapsed. His scholarship relied on first-hand accounts from emigres, census data and other official documents, Russian and other media accounts, economic data, and information that he gleaned from related fictional works.
After the Cold War, and after a long-standing ban on his works, Conquest's books were serialized or excerpted in Soviet publications. Writing in the journal Novy Mir, according to the New York Times, a reviewer of "The Harvest of Sorrow" wrote that "we, the compatriots of the innocents who perished, must be grateful to the English historian."
An aficionado of science fiction, Conquest found a connection between his historical work and his more private literary pleasure.
"A science-fiction attitude is a great help in understanding the Soviet Union," he told the Los Angeles Times. "It isn't so much whether they're good or bad, exactly; they're not bad or good as we'd be bad or good. It's far better to look at them as Martians than as people like us. George Orwell said that it needs an effort of the imagination as well as of the intellect to understand the Soviet Union."
George Robert Acworth Conquest was born in Great Malvern on July 15, 1917. His family was prosperous, dividing time between England and France, before losing much of its wealth in the Depression.
Conquest was educated at Winchester College in England, the University of Grenoble in France and Magdalen College at Oxford, where he did his undergraduate training in philosophy, politics and economics and his advanced studies in Soviet history.
At Oxford in the late 1930s, he said, he found the other communists "very dull and rather stupid." He recounted to the London Guardian, "I asked, 'Comrade, what is the party line if the Chamberlain government goes to war with Hitler?' And he said, 'Comrade, that will never happen.' I thought, 'Oh, no.' "
During World War II, Conquest joined the Oxfordshire and Buckinghamshire Light Infantry. He was recruited for a course in Bulgarian and was sent behind enemy lines in Bulgaria, where he later served in the British Foreign Office.
After the war he did stints in the British Information Research Department, which countered Soviet propaganda, and with the United Nations, before pursuing his writing full time.
Conquest's poetic work included editing "New Lines" (1956), a collection of verses by poets including Thom Gunn and Kinglsey Amis — with whom Conquest wrote the novel "The Egyptologists" (1965) — and Philip Larkin. Conquest's poems were collected in numerous volumes over the decades, including "Penultimata" (2009) and "Blokelore & Blokesongs" (2012).
In his academic work Conquest was associated with several universities in the United States before joining the Hoover Institution at Stanford University in 1977. His early books on Russia included "Common Sense About Russia" (1960), "Power and Policy in the U.S.S.R." (1961) and "Russia After Khrushchev" (1965).
He wrote biographies of Stalin and Lenin, the founder of the Soviet Union, and volumes including "Where Marx Went Wrong" (1970), "Kolyma: The Arctic Death Camps" (1978) and "Inside Stalin's Secret Police" (1985).
More recently, Conquest published sweeping works of history, including "Reflections on a Ravaged Century" (2000) and "The Dragons of Expectation: Reality and Delusion in the Course of History" (2005).
In England, he was an adviser to leaders including Prime Minister Margaret Thatcher. In the United States, he testified before the Senate about weaknesses of the Soviet leadership. His awards included the Presidential Medal of Freedom, the nation's highest civilian honor, which was bestowed in 2005 by President George W. Bush, and the Order of the British Empire.
Conquest's marriages to Joan Watkins, Tatiana Mihailova — whom he shepherded out of Bulgaria during the early years of the Cold War — and Caroleen MacFarlane ended in divorce.
Survivors include his wife of 36 years, the former Elizabeth Neece, of Stanford; two sons from his first marriage, John Conquest of Spring, Texas, and Richard Conquest of Noyant-la-Plaine, France; a stepdaughter, Helen Beasley of Hollister, California; and five grandchildren.
Perhaps as a release from the grim nature of his historical writing, Conquest enjoyed penning light verse. At times, his two writing worlds collided, such as in these lines:
There was a great Marxist named Lenin
Who did two or three million men in.
That's a lot to have done in,
But where he did one in
That grand Marxist Stalin did ten in.
