The Islamic State has claimed responsibility for a planned attack Friday night by gunmen and bombers that killed more than 120 people and injured many others at various locations across Paris. French President Francois Hollande has called the assault an act of war against France, and the country has declared a state of emergency.

In February 1996, on a Sunday evening, I was sitting in the living room of the parish in London in which I served, with a couple of the other priests. We were watching television, having a beer, relaxing after a busy weekend.

Suddenly, and quite clearly, we heard an explosion, or at least something that sounded like an explosion. None of us had ever actually heard a bomb go off.

Later, we heard on the news that an IRA operative had scored what the English wittily call an “own goal” — his bomb had prematurely exploded on a London double-decker bus — from New Cross, not far from my parish.

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Jump forward to last year when Prince Charles, the heir to the British throne, in a remarkable display of the “stiff upper lip,” shook hands with Martin McGuiness, the deputy First Minister of the Northern Ireland Assembly and a former member of the IRA, which blew up Charles’ beloved mentor, Lord Louis Mountbatten.

It is commonly understood and accepted, by the chattering classes, that “yesterday’s terrorist is today’s government leader,” and there is much truth to that statement.

Think of McGuiness, so many others — even, it has to be said, Nelson Mandela. The Northern Ireland Agreement; the peace accord between the Spanish government and the terror group ETA; negotiations between the ANC and the South African government — all of these depended on a dialogue based at least in part on compromise, territorial and cultural ambitions that had to be brokered, and, in the end, some kind of reason.

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ISIS, al Qaeda, Boko Haram or any number of the examples of Islamic extremism spreading across the globe unfortunately fail to fit any of those categories, least of all the use of reason. Islamic violence, which is, as the leading Catholic scholar of Islam, the Egyptian Jesuit the Rev. Samir Khalil Samir, has pointed out, a “legitimate” understanding of both the Koran and the teachings of the prophet Mohammed — this cannot be reasoned with, negotiated with nor even engaged in dialogue.

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The only dialogue this widely popular understanding of the tenets of the prophet accept — what was offered to the Christians of Mosul whom I met in Iraq earlier this year — is “convert or die.”

The secular West, and the elites who control government, media and academia, especially in Europe and increasingly so here in the United States, simply cannot comprehend the danger of militant Islam. One almost feels sorry for them.

I am reminded of hearing recently of the Archbishop of Canterbury talking about the power of sitting opposite a member of ISIS and engaging in dialogue — presumably over a lovely cup of Earl Gray tea and a piece of Dundee cake. Sadly, by the time the archbishop’s lips reached the cup, his head would be rolling across the floor of Lambeth Palace.

This is about religion. It is about a clash, both of civilizations and cultures.

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But the secular mindset, which finds religion, especially Christianity — “those people who cling to their guns and their religion” — incomprehensible, cannot see this as an apocalyptic death cult. This is certainly what ISIS is, and it will not respond to reason, debate, dialogue — or tea.

Western civilization must remember and value its past, and stop apologizing for it. We must demand those who wish to emigrate, or find shelter in the West, willingly embrace the Christian basis of society and assimilate. They must fight with great power and sacrifice to at least quell, as we have done in the past, the forces of Islamic extremism, or the West, as we have known it, is finished.

Father Benedict Kiely is a Catholic priest and founder of Nasarean.org, which is helping the persecuted Christians of the Middle East.