So what might animate a U.S.-Russian alliance? The core focus can and should be stability and mutual security in and around the Eurasian land mass. This has three aspects. First, as Alexander Vershbow, the current U.S. ambassador in Moscow, puts it: "Russia is the most important key to the stability of Eurasia" itself, without which neither Europe nor Asia, two regions in which the United States has vital interests, can "be stable and prosperous." As long as Russia respects the sovereignty of the former Soviet republics, the United States has every reason to cooperate with Russia in stabilizing and aiding those states. In this regard, as well as others, alliance does not mean condominium; U.S.-Russian collaboration must not imply a readiness to decide matters over the heads of Russia's neighbors. On the contrary, an alliance's purpose would be to strengthen their sovereignty and vitality. One example of the subtle way in which the revolution in Russian foreign policy makes this kind of alliance possible concerns Belarus. Putin's new agenda has led to a sharp cooling in Russia's relations with Alexander Lukashenko's regime. As a consequence, a leadership that flouts the values on which modern European security is based is increasingly isolated, the prospect of a Russian-Belarusian union has faded and Ukraine's fears of encirclement have eased. Although not perfectly parallel, U.S. and Russian interests in Belarus, Ukraine and Moldova now converge sufficiently to make promoting stability and successful reform there a matter of common U.S. and Russian ground.

Second, to borrow the formulation of Alexei Bogaturov, in the 21^st century no longer is peninsular Europe or Northeast Asia the critical "strategic rear" of the United States, but the vast turbulent region stretching from eastern Turkey to western China and along Russia's south. As the United States girds to cope with the threats emanating from this area, no country brings more value as a potential ally than Russia. As things stand, the United States has backed into Central Asia with military power as part of the war against terrorism, and in the process it has offered quasi-security commitments to its new partners, almost certainly without careful consideration of their wider implication. Central Asia forms the unstable core of Inner Asia; it is an area-the only one in the world-surrounded by four nuclear powers, two of whom recently teetered on the brink of war. It contains multiple points of friction, from Kashmir to the Fergana Valley to northwest Kazakhstan to China's Xinjiang province, each of them capable of bleeding into a larger conflict. It is populated by regimes whose stability is universally suspect. And it contains wealth, particularly in energy resources, that will make it increasingly important to both Asian and European consumers.

Not only, therefore, are the United States and Russia directly but separately implicated in the stability of the region, but a third country, China, is as well. This raises the third aspect of a U.S.-Russian alliance to enhance Eurasian stability. China will be a decisive actor in Inner Asia, not the least because it forms an integral part of the region. Unfortunately, China enters through its underdeveloped northwest territories, including Xinjiang, precisely where it feels most vulnerable. In part because of this sense of vulnerability, and in part because of the general state of Sino-American relations, China has not welcomed the arrival of American military power in Central Asia. On the contrary, while excusing a temporary deployment in the context of a war that it supports, China's leadership has opposed an extended U.S. presence there as an element of a hostile encirclement stratagem.

Russia and the United States have good reason to act jointly, not only to enhance their common stake in regional stability, but to draw China into a constructive dialogue over the role all three will play in Central Asia. Russia, with the Shanghai Cooperation Organization, is already engaged in such an effort. Talking to the Russians about U.S. military activities in Central Asia (and Georgia) builds mutual confidence by promoting transparency, but it is not so far-fetched to imagine a far more ambitious trilateral dialogue among Russia, China, and the United States. Much as the United States and its European allies share assessments of threats at the edges of Europe, plan for coordinated action, and struggle to create the necessary machinery, so can and should Russia and the United States do the same in Eurasia, with Chinese participation when appropriate.

Russia and the United States allied against the new century's primary strategic threats, particularly those emanating from within and around the Eurasian land mass, would have much the same significance in the emerging international order as key U.S. alliances have had in the last. Even more so will this be the case if the alliance is underpinned by Russia's successful integration into the international economy and safe passage to democracy.

Robert Legvold is professor of political science at Columbia University and editor of the forthcoming Thinking Strategically: The Major Powers, Kazakhstan, and the Central Asian Nexus (The MIT Press).