An American century is upon us. The US's military strength is unmatched, its technological advantage unbridgeable. Arms races are a thing of the past, as no one can compete with the giant. And, under this benign but distant hegemony, the world is at peace.

What's wrong with this picture?

This vision has been around for some time, but has had a lot of circulation recently. The vision is imperialist in the literal sense of the world: it sees the peace and happiness of the world as guaranteed by the continual dominance of an American Empire in the economic, political, and military fields. On the first two fronts, many skilled commentators have argued either side of the case. But on the third front, this vision is flat-out wrong: the salvation of the world does not lie in the armies of America. And the reasons for that have nothing to do with politics, or social trends, or the vagaries of international diplomacy. They have to do with science and technology.

The first intercontinental Ballistic missiles were deployed at the end of the fifties. Now, in 2005, there still is no defence against them. The American "National Missile Defence" is a joke (unreliable, only tested successfully in unrealistic "ideal" conditions, and a very poor success rate even then), and will remain so for years to come. More worryingly, even though no such defence system is operational, governments have already come up with ways to counter them; multiple war-heads, decoys, various jamming techniques, etc..., which mean that the deployment of a system capable of countering the threats of today is decades in the future. By which time, of course...

Out of context, this might seem like a minor, technical point; yes this technology is more advanced than that one, but what so what? But this is just the most visible part of a trend that underlies the ultimate futility of a military strategy. As has been pointed out before, if one country can blow up the world twice while its competitor can only blow it up once, you can't say that the first country enjoys much of an advantage.

The crux is the second law of thermodynamics, and its concept of entropy. The exact concept is highly technical, subtle and mathematical. However its effect on military technology can be paraphrased as: destroying things is easy. Fixing or protecting them is not. And the more advanced the world becomes, the more energy and means countries have at their disposal, the more that difference will become evident.

In fact, the offensive has always outstripped any defensive measures, from the moment that warfare was released from physical strength and replaced with the chemical energy of the first gun. Weapons get more and more destructive, and defences mitigate, rather than counter, their effects. Artillery forced armies to increase in size, spread out and extend the scope of the battlefield, but the humble artillery shell was never shot down or countered. Second World War bombers were shot down by fighters, ground fire or missiles, but no combatant ever claimed to have turned the clock back on bombers, or that their cities had been made safe from them. And as any physicist or engineer an tell you, it requires much more work and power to protect something that to destroy it; and the more advanced we become, the more the gulf between offence and defence grows. And now, there is no room to grow the battlefield, that last defence against new weapons: from the point of view of ICBM's, the entire world is the battlefield.

At a comparatively small effort to themselves, China, Britain and France can easily modernise their arsenals to get round any defensive system the United States could assemble, at a fraction of the cost - probably using the very spin-off technologies that an American investment in armaments is sure to generate around the world.

Russia could cause the USA untold devastation (nuclear winters, global economic collapse, radiation clouds circling the globe) if it were to detonate its nuclear weapons on its own territory - the biggest suicide bombing in history. And no military solution could ever stop this.

The logic of MAD (mutually assured destruction) was never that opponents were equal, just that they could inflict unacceptable levels of damage on each other - and this is the case for all major military powers, and will continue to be the case no matter how much the US military expands. So if this expansion is not to combat the major military powers, what is it for?

Ah, but proponents of American military power will argue, retreating slightly from the full pax americana, the new nuclear weapons and missile shields will at least maintain peace with so-called rogue states - all those dangerous or potentially dangerous countries outside the standard world order.

And indeed, military power will continue to be powerful against rogue states and minor powers, at least for the next few decades. But its utility is fast running out. North Korea, a country so poor its main export is its fleeing population, has produced missiles that the USA, the world's superpower, cannot intercept. Many rogue and second tier states are fast developing nuclear weapons and ways of delivering them. And if the Americans military finds a way of protecting itself against the current generation of missiles - well, it won't take much effort to upgrade to whatever's needed to get around that.

The ultimate goal for these states is the equivalent of the Russian self-destruction a deterrent that cannot be countered, whatever the cost to the initiating country. Doctor Strangelove's doomsday machine is a fiction - but one that probably isn't too far off. As time goes on, the number of countries that can apply the logic of MAD to the rest of the world will steadily increase.

More importantly, research into missile shields or more destructive weapons on the part of America is the most foolish route to pursue. For rogue states do not develop their weapons in a vacuum. They depend very much on the direct or indirect "trickle-down" of military technology from stronger powers - from the United States, to some extent, but also from the other major military powers, Russia, UK, France, China, Israel, even India and Pakistan. And so far this century, there has a been a remarkable and effective moratorium on developing weapons beyond the hydrogen bomb, or real research into more advanced long ranged missiles. The reasons for this moratorium rested on the MAD logic - there was no need to improve their nuclear arsenal, so development shifted to conventional weapons, rapid-reaction forces, intelligence and precision weapons.

So the worst thing that can be done is to encourage these countries to break this moratorium, as the development of a missile shield on the part of the United States would undoubtedly do. To keep MAD alive, they would invest in more destructive weapons, improved delivery systems - and destructive nuclear technology would spread. This has nothing to do with the attitudes or politics of these states (though those could definitely worsen things), but with the inevitable and human fact that as more people in more countries know more technology, the chances of them spreading increase to certainty. Already tribal societies with no industrial base make Kalashnikovs, while anti-intellectual dictatorships with no research traditions develop nuclear weapons.

And even the USA's huge advance over the other major powers, and their respective huge advance over rogue states, will come to naught in front of the ever greater destructiveness of the next generation of weapons. For there is a lot of destructive room above the humble H-bomb.

So this is the situation. We have a window of maybe a few decades, maybe even a century, to bind rogue states to a political and economic global order. Not just rogue states, ultimately, but all countries, for any country left behind or outside is a potential rogue state. Beyond that, it will be too late; MAD will have spread to every corner of the planet, and any state that wishes to can keep all others away with a balance of terror. We are racing to avoid this apocalypse, spreading political and economic incentives before the window closes, before everyone gets these weapons and uses them - by accident or design.

And the current American actions - developing its nuclear arsenal, missile shield, forcing its enemies into arms races - are all contributing to shorten this crucial window, not only making political and economic progress much harder, but also hastening the coming of the day when America's military superiority becomes irrelevant.

We need to win the race against the apocalypse.