Frederick Forsyth has a good article on why the doctrine of pre-emptive war has become necessary in the wake of 9/11.

Until the mid-1990s, terrorists always wanted something. The IRA wanted a united Ireland, the ETA wanted a separate Basque state, the PFLP wanted a Palestinian state and the extirpation of Israel, the Tamil Tigers wanted a Tamil state in part of Sri Lanka...and so on.

Some wanted separation, some unification, some (like the Kurds) a state of their own, others (like the Red Brigades) a fully communist state. Precisely because of that, they wanted to stay alive and see their vision come true, and therefore the Establishment could, if it wished, negotiate.

Then a small group arose who said this: "We do not want anything of you but your deaths. In thousands, in hundreds of thousands and eventually in millions.

"We say this because we hate you. We hate you with an all-consuming passion, not just for what you have done (though that is bad enough) but for what you are.

"There is no point in negotiating, for there is nothing to negotiate. We are going to kill you whenever, wherever and in as great a number as we can.

"We do this because the Almighty has commanded it. We have His texts to prove it. We do not fear death, we welcome it, for we are guaranteed eternal bliss if we die while killing you."

It was a weird message. It did not come in the mail, nor was it enunciated on Al-Jazeera television. It came from a thousand imams in a thousand mosques. It was directed at the United States in particular and the West in general. Its source can best be described as Islamist fundamentalism, a tiny but virulent incubus within the body of that great, billion-devotee religion, Islam. Not unnaturally, no one took it particularly seriously – at first.

It's well worth a read. Check it out here.