Not so fast. The world is not at the brink of nuclear peace. For one thing, START II is conditioned on implementation of the START I agreement signed by George Bush and Soviet President Mikhail Gorbachev in July 1991. But that treaty is still unendorsed by two of the three non-Russian republics that possess elements of the old Soviet nuclear arsenal, and neither Washington nor Moscow will allow it to take effect absent the republics’ compliance. For another START II itself may well encounter resistance from conservative nationalists in the Russian Parliament, on the ground that it gives the store away: it calls for the elimination of Russia’s greatest nuclear strength-land-based multiple-warhead missiles-while leaving essentially intact the United States’ most threatening nuclear system, its submarine-based ICBMs. In addition, the treaty is necessarily silent on nuclear proliferation elsewhere in the world, even though that may become the most pressing arms-control problem. Finally, nothing in START II addresses the central strategic issue for the incoming Clinton administration: does the U.S. nuclear arsenal still have a role in a post-cold-war environment? If so, in what form should those weapons be deployed?

If the tortuous history of arms control offers any clear lesson, it is this: nuclear weapons are ultimately political instruments, not military ones. Useless for purposes of actual warfare, they are still taken as the ultimate guarantor of national sovereignty. This is one reason Ukraine, Belarus and Kazakhstan have become obstacles to START II. The first two have signed neither START I nor the 1968 NonProliferation Treaty (NPT), a 148-nation protocol on control of nuclear material, approval of which by the republics is another joint U.S.-Russia condition for implementation of the agreed arms reductions. Kazakhstan has endorsed START I but not NPT. In each case, there is concern over loss of security relative to Russia. The conventional wisdom says Belarus and Kazakhstan will sign up, but there is no such confidence about Ukraine, despite assurances of “full support” last week from its foreign minister, Anatoly Zlenko.

Ukraine is in a unique position: it genuinely fears a resurgence of Russian nationalism that could pose a military threat to the Kiev government. It believes that a nuclear Ukraine would have some deterrent capability against Russian conventional forces, and argues that the price for surrendering its nuclear forces must be both Western financial aid and a security guarantee from NATO. But the Atlantic alliance wants nothing to do with protecting Ukraine-compared with which intervention in the war for Bosnia would be a cakewalk. In any case, NATO’s nuclear forces were designed with specific threats to alliance members in mind.

Which raises the fundamental question: who does need nuclear weapons in the post-cold-war world, and why? It’s been a mostly academic topic so far, but Bill Clinton can hardly avoid it. It is always comforting to stick with long-held premises, and the prevailing belief inside the U.S. national-security community is that for perhaps the next generation the future of nuclear strategy will be much like the past. A residual Russian nuclear arsenal of 3,000 warheads under START II will still require the United States to maintain a “minimum deterrence” capacity: 3,500 warheads under the treaty, or enough to hit all critical military, industrial and leadership targets even after absorbing a first strike. The assumption here is that U.S. forces must be structured for a prolonged nuclear conflict.

Against this is the view that the possibility of superpower nuclear exchange “has receded to the vanishing point,” in the words of Les Aspin, Clinton’s defense secretary-designate. As a result, he argued in two speeches last year, the U.S. interest in nuclear-weapons possession has “literally reversed.” During the cold war, the U.S. nuclear capability served as a counterweight to Soviet conventional forces. It was deemed necessary, for example, to deter any Soviet invasion of Western Europe. But with the collapse of the Soviet military, the United States is now the world’s dominant conventional power. Countries that wish to resist it will inevitably be tempted to develop nuclear capacities as a similar kind of counterweight. “Nuclear weapons are still the big equalizer,” Aspin said, “but now the United States is not the equalizer but the equalizee.” If that implies a direct and urgent American interest in nonproliferation, it may also suggest an interest in nuclear reductions well below those agreed to last week.