Samuel P. Huntington – a longtime Harvard University professor, an influential political scientist, and mentor to a generation of scholars in widely divergent fields – died Dec. 24 on Martha’s Vineyard. He was 81.

Huntington had retired from active teaching in 2007, following 58 years of scholarly service at Harvard. In a retirement letter to the President of Harvard, he wrote, in part, “It is difficult for me to imagine a more rewarding or enjoyable career than teaching here, particularly teaching undergraduates. I have valued every one of the years since 1949.”

Huntington, the father of two grown sons, lived in Boston and on Martha’s Vineyard. He was the author, co-author, or editor of 17 books and over 90 scholarly articles. His principal areas of research and teaching were American government, democratization, military politics, strategy, and civil-military relations, comparative politics, and political development.

“Sam was the kind of scholar that made Harvard a great university,” said Huntington’s friend of nearly six decades, economist Henry Rosovsky, who is Harvard’s Lewis P. and Linda L. Geyser University Professor, Emeritus. “People all over the world studied and debated his ideas. I believe that he was clearly one of the most influential political scientists of the last 50 years.”

“Every one of his books had an impact,” said Rosovsky. “These have all become part of our vocabulary.”

Jorge Dominguez, Harvard’s vice provost for International Affairs, described Huntington as “one of the giants of political science worldwide during the past half century. He had a knack for asking the crucially important but often inconvenient question. He had the talent and skill to formulate analyses that stood the test of time.”

Huntington’s friend and colleague Robert Putnam, the Peter and Isabel Malkin Professor of Public Policy at the Harvard Kennedy School, called him “one of the giants of American intellectual life of the last half century.”

To Harvard College Professor Stephen P. Rosen, Beton Michael Kaneb Professor of National Security and Military Affairs, “Samuel Huntington’s brilliance was recognized by the academics and statesmen around the world who read his books. But he was loved by those who knew him well because he combined a fierce loyalty to his principles and friends with a happy eagerness to be confronted with sharp opposition to his own views.”

Huntington, who graduated from Yale College at age 18 and who was teaching at Harvard by age 23, was best known for his views on the clash of civilizations. He argued that in a post-Cold War world, violent conflict would come not from ideological friction between nation states, but from cultural and religious differences among the world’s major civilizations.

Huntington, who was the Albert J. Weatherhead III University Professor at Harvard, identified these major civilizations as Western (including the United States and Europe), Latin American, Islamic, African, Orthodox (with Russia as a core state), Hindu, Japanese, and “Sinic” (including China, Korea, and Vietnam).

“My argument remains,” he said in a 2007 interview with Islamica Magazine, “that cultural identities, antagonisms and affiliations will not only play a role, but play a major role in relations between states.”

Huntington first advanced his argument in an oft-cited 1993 article in the journal Foreign Affairs. He expanded the thesis into a book, “The Clash of Civilizations and the Remaking of World Order,” which appeared in 1996, and has since been translated into 39 languages.

To the end of his life, the potential for conflict inherent in culture was prominent in Huntington’s scholarly pursuits. In 2000, he was co-editor of “Culture Matters: How Values Shape Human Progress.” And just before his health declined, in the fall of 2005, he was beginning to explore religion and national identity.

“His contributions ranged across the whole field of political science, from the deeply theoretical to the intensely applied,” said Putnam, author of a lengthy appreciation of Huntington in a 1986 issue of the journal PS: Political Science and Politics. “Over the years, he mentored a large share of America’s leading strategic thinkers, and he built enduring institutions of intellectual excellence.”

And Putnam added a personal note. “What was most rare about Sam, however, was his ability to combine intensely held, vigorously argued views with an engaging openness to contrary evidence and argument. Harvard has lost a towering figure, and his colleagues have lost a very good friend.”

Timothy Colton, the Morris and Anna Feldberg Professor of Government and Russian Studies at Harvard, remarked on his old friend’s breadth of intellectual interests. He used the American political experience as a pivot point (Huntington’s doctoral dissertation was on the Interstate Commerce Commission), but soon deeply studied a globe-spanning range of topics.

“He was anchored in American life and his American identity, but he ended up addressing so many broad questions,” said Colton, who had Huntington as a Ph.D. adviser at Harvard in the early 1970s. “His degree of openness to new topics and following questions where they take him is not as often found today as when he was making his way.”

Huntington’s first book, “The Soldier and the State: The Theory and Politics of Civil-Military Relations,” published to great controversy in 1957 and now in its 15th printing, is today still considered a standard title on the topic of how military affairs intersect with the political realm. It was the subject of a West Point symposium last year, on the 50th anniversary of its publication.

In part, “Soldier and the State” was inspired by President Harry Truman’s firing of Gen. Douglas MacArthur – and at the same time praised corps of officers that in history remained stable, professional, and politically neutral.

In 1964, he co-authored, with Zbigniew Brzezinski, “Political Power: USA-USSR,” which was a major study of Cold War dynamics – and how the world could be shaped by two political philosophies locked in opposition to one another.

Brzezinski, a doctoral student at Harvard in the early 1950s who was befriended by both Huntington and Rosovsky, was U.S. National Security Adviser in the Carter White House from 1977 to 1981. In those days, said Rosovsky, the youthful Huntington, though an assistant professor, was often mistaken for an undergraduate.

According to his wife Nancy, Huntington was a life-long Democrat, and served as foreign policy adviser to Vice President Hubert Humphrey in his 1968 presidential campaign. In the wake of that “bitter” campaign, she said, Huntington and Warren Manshel – “political opponents in the campaign but close friends” – co-founded the quarterly journal Foreign Policy (now a bimonthly magazine). He was co-editor until 1977.

His 1969 book, “Political Order in Changing Societies,” is widely regarded as a landmark analysis of political and economic development in the Third World. It was among Huntington’s most influential books, and a frequently assigned text for graduate students investigating comparative politics, said Dominguez, who is also Antonio Madero Professor of Mexican and Latin American Politics and Economics. The book “challenged the orthodoxies of the 1960s in the field of development,” he said. “Huntington showed that the lack of political order and authority were among the most serious debilities the world over. The degree of order, rather than the form of the political regime, mattered most.”

His 1991 book, “The Third Wave: Democratization in the Late Twentieth Century” – another highly influential work – won the Grawemeyer Award for Ideas Improving World Order, and “looked at similar questions from a different perspective, namely, that the form of the political regime – democracy or dictatorship – did matter,” said Dominguez. “The metaphor in his title referred to the cascade of dictator-toppling democracy-creating episodes that peopled the world from the mid 1970s to the early 1990s, and he gave persuasive reasons for this turn of events well before the fall of the Berlin Wall.”

As early as the 1970s, Huntington warned against the risk of new governments becoming politically liberalized too rapidly. He proposed instead that governments prolong a transition to full democracy – a strand of ideas that began with an influential 1973 paper, “Approaches to Political Decompression.”

Huntington’s most recent book was “Who Are We? The Challenges of America’s National Identity” (2004), a scholarly reflection on America’s cultural sense of itself.

Samuel Phillips Huntington was born on April 18, 1927, in New York City. He was the son of Richard Thomas Huntington, an editor and publisher, and Dorothy Sanborn Phillips, a writer.

Huntington graduated from Stuyvesant High School, received his B.A. from Yale in 1946, served in the U.S. Army, earned an M.A. from the University of Chicago in 1948, and a Ph.D. from Harvard in 1951, where he had taught nearly without a break since 1950.

From 1959 to 1962, he was associate director of the Institute of War and Peace Studies at Columbia University. At Harvard, he served two tenures as the chair of the Government Department – from 1967 to 1969 and from 1970 to 1971.

Huntington served as president of the American Political Science Association from 1986 to 1987.

Huntington was director of Harvard’s Center for International Affairs from 1978 to 1989. He founded the John M. Olin Institute for Strategic Studies, and was director there from 1989 to 1999. He was chairman of the Harvard Academy for International and Area Studies from 1996 to 2004, and was succeeded by Jorge Dominguez.

Huntington applied his theoretical skills to the Washington, D.C., arena too. In 1977 and 1978, he served in the Carter White House as coordinator of security planning for the National Security Council. In the 1980s, he was a member of the Presidential Commission on Long-Term Integrated Strategy.

Huntington is survived by his wife of 51 years, Nancy Arkelyan Huntington; by his sons Nicholas Phillips Huntington of Newton, Mass. and Timothy Mayo Huntington of Boston; by his daughters-in-law Kelly Brown Huntington and Noelle Lally Huntington; and by his four grandchildren.

There will be a private family burial service on Martha’s Vineyard, where Huntington summered for 40 years.

In the spring, there will be a memorial service at Harvard. Details are pending.

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