[Angelino97]

Neoconservatives believe in a Clash of Civilizations? Since when?

Since always. I recall it being a popular Neocon talking point post 9/11, and one of the reasons given for why we must invade Iraq and Iran.

Have you forgotten all the Neocon war drums calling for war against Iran in the mid 2000s?

One Neocon eventually published a book with that title, in 2011, The Clash of Civilizations and the Remaking of World Order.

[rmlew]

I think you don't know what a neoconservative is (or rather became) and who Samuel Huntington was and what he believed in.
Unlike first generation neoconservatives, who included the likes of Jeane Kirkpatrick, the second generation went full Wilsonian with the end of the Cold War. Francis Fukayama famously wrote The End of History and the Last Man pushing liberal democratic universalism and rejecting the idea that Liberal Democracy and freedom were tied to any specific history and civilization. This zeitgeist was behind those who wanted to democratize Iraq and Afghanistan with no understanding of the nature of those countries, their history, or cultures.

Samuel Huntington was a JFK liberal on foreign policy, but also a WASP who wanted to maintain Anglo-America, believing that our liberty was tied to our cultural heritage. You really should read his last book Who Are We? The Challenges to America's National Identity, which was published in 2005. The Clash of Civilizations and the Remaking of World Order was published in 1996, and grew out of his work looking at the success and issues with democratizing countries, The Third Wave: Democratization in the Late Twentieth Century.

PS. I would suggest that you read Jim Kalb's Conservatism FAQ.