Russia and the United States recently signed a new strategic nuclear-arms reduction treaty (Start). Officially, the treaty cuts their weapons by one-third; in fact, each party will decommission only several dozen.

Nevertheless, the treaty is a considerable achievement. It normalises political relations between the two countries, thereby facilitating their further cooperation and rapprochement.

The return of strategic nuclear weapons to the center of world politics increases Russia's political weight and highlights the field in which Russia can still assert itself as a superpower. It also gives a political boost to Barack Obama, cast as the most constructive and progressive US President for decades, and possibly for many years to come.

After the treaty was signed, the US hosted a nuclear non-proliferation summit, a landmark event for the Obama Administration, which has made the fight against nuclear proliferation a trademark policy. The few accords reached at the summit, although welcome, are not as significant as the impression that the summit created that world leaders are ready to work together to confront nuclear proliferation.

But debates about the role of nuclear weapons in the modern world, as well as in the future, are only beginning.

The world system on which past discussions of nuclear weapons were based has become almost unrecognisable, calling into question the adequacy of the mentality and concepts inherited from that system.

The heart of the matter is this: It is obvious that nuclear weapons are immoral. An A-bomb is millions of times more immoral than a spear or sword, hundreds of thousands of times more immoral than a rifle, thousands of times more immoral than a machine gun, and hundreds of times more immoral than salvo systems or cluster bombs.

But nuclear arms also have a significant moral distinction: Unlike other weapons, they are an effective means of preventing the large-scale wars and mass destruction of people, property, and cultures that have plagued humanity throughout recorded history. To reject nuclear weapons and strive for their elimination is, no doubt, a moral aim, at least in the abstract. But it is feasible only if humanity changes.

Apparently, the advocates of eliminating nuclear weapons believe that such change is possible. I do not. Indeed, the risks of a world without nuclear weapons - or only a minimal number of them - are tremendous.

Nuclear deterrence - a threat to kill hundreds of thousands or millions of people - is a concept that does not fit into traditional morals.

Yet it has worked, preventing catastrophic wars while making people more civilized and cautious. When one pole of nuclear deterrence weakened, due to Russia's political decline in the 1990s, Nato, a defensive union of democratic and peaceful states, committed aggression against Yugoslavia. Now that Russia has restored its capability, such a move would be unthinkable. After Yugoslavia, there was an unprovoked attack on Iraq.

In a nearly perfect world, Russia and the US would not need large nuclear stockpiles. But cutting nuclear weapons to a bare minimum in the current conditions would give a big advantage to small nuclear powers, which will see their nuclear potential gain near-parity with larger states.

Moreover, reducing nuclear weapons to a minimum might theoretically enhance the usefulness of missile-defense systems and their destabilising role. And even non-strategic missile-defense systems, the deployment of which might be useful, will be questioned.

If stockpiles of tactical nuclear weapons are reduced, as some US, European, and Russian experts have proposed, the opponents of Russia's ongoing military reform will have even more reason to object to reconfiguring the country's conventional armed forces away from confrontation with Nato toward a flexible-response capability vis-à-vis other threats.

Similarly, if the US withdraws its largely nominal tactical nuclear weapons from Europe, US-Europe strategic ties would weaken. Many Europeans, above all in the new Nato member-states, would then demand more protection from the mythical Russian Leviathan.

The world community seems to be losing its strategic bearings. Instead of focusing on the real problem, namely the increasingly unstable international order, it is trying to apply Cold War-era concepts of disarmament. At best, these are marginally useful; more often, they are harmful in today's circumstances.

What is most needed nowadays is clear thinking about how to live with an expanding club of nuclear states while keeping the world relatively stable. To this end, the two great nuclear powers need a coordinated deterrence policy towards new nuclear states.

Simultaneously, they should offer guarantees to non-nuclear states that might feel insecure. In the first place, it is necessary to fill the increasing security vacuum in the Middle East. China, the world's rising strategic player, might join this policy, though it currently ranks third in terms of military power.

Arms-control talks are mostly needed for rendering national arsenals more transparent, and for building confidence between the great powers. That is all there is to their usefulness.

So, instead of mimicking Cold War-era treaties, it is necessary to launch an international discussion about the role of military force and nuclear weapons in the world as it is now evolving. We might then eventually recognize that eliminating nuclear weapons is not just a myth, but a harmful myth, and that nuclear weapons are a useful asset that has saved, and may continue to save, humanity from itself.

© Project Syndicate, 2010, www.project-syndicate.org

The author is Dean of the School of World Economics and Foreign Affairs at Moscow State University - Higher School of Economics.