The real reason why Russia and China aren’t interested in stopping Iran’s nuclear program.

As President Obama begins a push to impose harsher economic sanctions on Iran over its nuclear program, his success will be determined largely by the answer to a single question: Will China and Russia get on board? In order to bite, sanctions must be enforced by the rest of the international community, but, so far, Beijing and Moscow have been reluctant to endorse the toughest penalties advocated by Washington.

Many analysts and policymakers wrongly assume that this reluctance is a function of these countries’ economic ties with Iran, or their failure to appreciate the proliferation threat. Last week, for example, Hillary Clinton bluntly challenged China’s approach to Tehran, saying, “[W]e understand that right now it seems counterproductive to you to sanction a country from which you get so much of the natural resources your growing economy needs. But think about the longer term implications.” The real reason for Beijing and Moscow’s obstinacy, however, is much more fundamental, and from Washington’s point of view, much more distressing: China and Russia are not particularly threatened by, and may even see a significant upside to, a nuclear-armed Iran.

To understand this point, we must first consider why the United States, China, and Russia--or any other country for that matter--should fear nuclear proliferation. Of course, there are the concerns of accidental nuclear detonation, nuclear terrorism, or even nuclear war. But these are all extremely low probability events. The primary threat of nuclear proliferation is that it constrains the freedom of powerful states to use or threaten to use force abroad.

The United States’ global power-projection capability provides Washington with a significant strategic advantage: It can protect, or threaten, Iran and any other country on the planet. An Iranian nuclear weapon, however, would greatly reduce the latitude of its armed forces in the Middle East. If the United States planned a military operation in the region, for example, and a nuclear-armed Iran objected that the operation threatened its vital interests, any U.S. president would be forced to rethink his decision. As then-Secretary of Defense Donald Rumsfeld explained in 2001, nuclear weapons “could give rogue states the power to hold our people hostage to nuclear blackmail--in an effort to prevent us from projecting force to stop aggression."

This line of thinking is not unique to the situation with Iran. In nearly every historical instance of proliferation, beginning with China in the 1960s, the United States opposed nuclear proliferation in large part because it wanted to preserve its military freedom of action. Indeed, the 2008 National Defense Strategy issued by the Pentagon explicitly states that the American military will achieve its objectives by “shaping the choices of key states, preventing adversaries from acquiring or using WMD, strengthening and expanding alliances and partnerships, securing U.S. strategic access and retaining freedom of action."