Russia and the United States have signed a new strategic nuclear-arms reduction treaty. Officially, the treaty cuts their weapons by one-third. In reality, each party will decommission only several dozen.

Nevertheless, the treaty is a considerable achievement. It normalizes 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 it 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 that 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: 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 unrecognizable, 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.