In 1986, Soviet leader Mikhail Gorbachev offered his vision of a nuclear-free world. Gorbachev’s “new thinking” helped reverse the nuclear arms race and spark a series of agreements reducing strategic arsenals.

Nearly a quarter-century later, the Russian leadership has returned to reliance upon the doctrine of nuclear deterrence. While Russian leaders do not challenge President Obama’s long-term vision of a world free of nuclear weapons, and Russia continues to negotiate new agreements to reduce nuclear weapons stockpiles, nuclear deterrence is even more entrenched in the thinking of the Russian security community today than during the Cold War. There are at least two reasons for this.

First, Russia is a relatively weak conventional military power. In Gorbachev’s days, the Soviet Union deployed more tanks than the rest of the world’s countries combined and kept half a million men in a high state of readiness in Eastern Europe. A decade later, when Russian leader Vladimir Putin wished to suppress Chechen separatism, he found amid a million-strong military that the genuinely capable force numbered only about 65,000. Since the end of the Soviet Union, China has been buying many more Russian combat aircraft than Russia’s own air force.

Russia’s current military reform is far more successful at dismantling the existing military organization than at building its 21st-century successor. For the first time ever, Russia is a conventional military underdog on both of its strategic flanks, in Europe and Asia. Nuclear deterrence is Moscow’s answer to that strategic dilemma.

Second, Russia insists on retaining the strategic independence that characterizes a great power. This requires a rough equality between U.S. and Russian nuclear arsenals. Absent nuclear weapons, the Russo-American military equation becomes heavily skewed in favor of the United States.

To put it differently: If other factors remain unchanged, a world free of nuclear weapons is a world safe for U.S. conventional military hegemony. Less obvious but equally true, Russia’s nuclear advantage over its Chinese neighbor balances China’s increasing conventional strength. The price of “great-powerdom,” for Russia, is dependence on nuclear weapons, acceptance of the inherent insecurity they bring, and reliance upon nuclear deterrence. But advances in military technology hold the potential to upset this equation.

Russia therefore links its endorsement of strategic arms reductions to constraints on new technologies such as missile defenses and what it calls “weaponization of space.” Both are areas where the United States is perceived as holding the advantage. Russia also advocates expanding the U.S.-Russian strategic dialogue to include China.

A crucial step here would be to link U.S. and Russian missile defenses in a joint system. This would obviate reliance on mutually assured destruction. Deterrence would, at last, become a thing of the past. In principle, the Russian government favors cooperation toward this goal. For the moment, however, it lacks a clear strategy of reaching the new strategic world.

A world free from nuclear weapons would be a world transformed. Such a world would require mutual trust among the major powers (above all, the United States, Russia, and China), cooperation on strategic defenses, and a wide-ranging security collaboration among them that would consign conventional military balances (and imbalances) to history.

This is a tall order by any standard. Yet without it a world free from nuclear weapons will remain a dream — or a nightmare.