In the wake of Mr Cook’s historic resignation, the first from a Blair Cabinet on a point of principle, the archives are being ransacked for parallels. Indeed it’s getting pretty busy in the history section of every library at the moment as those who’re trying to make sense of momentous events reach for the past as their guide to the future.

But in judging what will happen during any war in Iraq, and what should follow, I believe we should not defer to history. Because the events now unfolding are truly revolutionary. Many of the assumptions with which policy-makers and commentators have grown up in the past 50 years are being transformed. If you want an historical comparison, then the events of our time now challenge the perceptions of governing elites as comprehensively as the French Revolution shattered the harpsichord and porcelain worldview of the ancien régimes. Concepts such as national sovereignty, deterrence and realpolitik, indeed our inherited perceptions of war itself, are being superseded by new realities. The fixed points by which statesmen have steered their nations for years are now lost in the desert storm.

One of the most cherished of those fixed points, respect for national sovereignty, is no longer a reliable guide to action. The whole postwar settlement, exemplified by the United Nations, was based on the belief that peace was best guaranteed by respecting the boundaries of nation states. Whatever horrors might emerge in one state, it was believed that far greater costs would ensue if the international consensus in favour of respecting each other’s borders broke down.

Admirable as this principle may be, it has proved deeply problematic in practice, as the American neo-conservative thinker Lee Harris has powerfully argued. Tyrants are protected as much as democracies, left at liberty to terrorise their own populations, free to practise genocide, insulated from the consequences of their own wickedness. It is left to the free nations of the West to absorb the population flows of desperate refugees, be held responsible for providing humanitarian relief, and then face condemnation from a chorus of delinquents at the UN General Assembly for not doing even more to prop up their mates.

If that were the only price the West had to pay, it may be supportable to ensure the stability which guaranteed sovereignty is believed to bring. But that stability, if it ever really existed, is now gravely threatened by the exploitation of inviolable borders by regimes such as Iraq, Iran and North Korea. Behind the barriers which we have erected for them, these states harbour terrorists and develop weapons of mass destruction. If we were to continue to respect the founding logic of the UN, we would meekly accept the right of any state to follow its path, building up its own nuclear arsenal, training its own terrorist cadres, because we dare not breach the boundaries of sovereignty to stop it.

What makes such a course not just fraught, but unthinkable, is the erosion of another familiar geopolitical landmark, the principle of deterrence. The combination of proliferating weapons of mass destruction and fanatical terrorism now means that a regime, if it were so minded, could detonate a device killing millions and leaving no fingerprints. Given the capacity of regimes to unleash devastation at a deniable distances we would not know how to respond, because we could not know with assurance whom to attack in retaliation. Deterrence depends upon a measure of certainty, certainty that an attacked state will respond, because it can be certain that it knows where an attack has come from. That certainty prevailed in the Cold War, it is wholly absent now.

One of the reasons it is absent is the disappearance of the third factor in international relations by which our leaders once navigated, the power of realpolitik. In the past, leaders pretty much knew that, however wicked their antagonists, they were still calculating actors who operated within the bounds of reason.

That assumption no longer holds after September 11. The terrorists behind that atrocity do not have a defined set of foreign policy goals which we can enter into negotiations on. They are ideological fanatics whose hatred for the West is total. They cannot be reasoned with, bought off, or deterred, not least because their own personal annihilation is part of the dream they chase. They seek not just the removal of American troops from the Gulf and the eradication of Israel, but the endless humiliation of the Great Satan.

These three developments together constitute a different world from the one into which most of us were born. The development of state sovereignty into a prime cause of instability, the impossibility of deterrence against new threats, and the appearance of enemies who will not subscribe to the calculations of realpolitik have brought us to a time when old rules must, perforce, be broken.

In this perilous new world I’m convinced that pre-emptive action is the least risky of all the options which face us. But given just how revolutionary and dangerous I believe our situation is, it is incumbent on all of us at least to listen to others who see a different way out of our problems. We have few certainties by which to steer. So let us stick to one, the assurance that we can always learn from civilised dialogue, and so respect what Mr Cook now has the freedom to tell us from the back benches.

michael.gove@thetimes.co.uk

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