WASHINGTON, Dec. 27 (Xinhua) -- Influential U.S. political scientist and "Clash of Civilizations" author Samuel Huntington has died at the age of 81, Harvard University announced Saturday on its website.

    Huntington, who retired from active teaching at Harvard in 2007,died on Dec. 24 in Martha's Vineyard, Massachusetts, the university said. It did not give the cause of his death.

    Huntington was best known for his theory on the so-called clash of civilizations. He believed that post-Cold War violent conflicts would come from cultural and religious differences rather than ideological rifts between nation states.

    He first made the argument in a 1993 article for the Foreign Affairs journal and then expanded it in his 1996 book "The Clash of Civilizations and the Remaking of World Order," which has been translated into 39 languages.

    "The Clash of Civilizations" theory has been hotly debated by academics and the general public especially after the 9/11 terrorist attacks in 2001.

    "Sam was the kind of scholar that made Harvard a great university," Huntington's long-time friend, economist Henry Rosovsky, was quoted by the website as saying.

    "People all over the world studied and debated his ideas. I believe that he is clearly one of the most influential political scientists of the last 50 years," Rosovsky said.

    Huntington 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.

    A life-long Democrat, Huntington served in the White House under President Jimmy Carter in the National Security Council in 1977 and 1978.

    Born in New York City on April 18, 1927, Huntington received his bachelor's degree from Yale University in 1946, served in the U.S. Army, then earned a Master's degree from the University of Chicago in 1948. He obtained his doctorate in 1951 from Harvard, where he had taught nearly without a break since 1950.

    He is survived by his wife of 51 years, Nancy Arkelyan Huntington, and two sons.