During the Communist era, Russia and China became ideological rivals. But since the Soviet collapse in the 1990s, Beijing and Moscow have strengthened diplomatic, economic and military ties. Last month, thousands of Chinese and Russian troops carried out unprecedented joint war games.

When China and Russia conducted joint military exercises in August, officials from both countries praised them as a sign of their new strategic partnership.

Chinese and Russian generals sought to reassure the world that the exercises were not aimed at any third nation. But some experts say the war games raise questions about whether closer Sino-Russian military ties are benign--or potentially threatening to the United States and the region.

Evan Medeiros, a China security expert at the research group in Washington D.C., says although Sino-Russian relations are at a turning point, Moscow is actually looking for a way to get Washington to cooperate more.

"Russia clearly has frustrations in its relationship with the United States and it can use its bilateral ties and its military aid to China as a way to leverage greater cooperation from the United States."

Bonnie Glaser is a China scholar at the Center for Strategic and International Studies in Washington D.C.

She says neither China nor Russia can afford to antagonize the United States. "The extent of collaboration between the two countries against the United States I think is not likely to be very great because it doesn't serve either Moscow or Beijing's interests."

But experts agree that Russia and China are concerned about U.S. dominance in global affairs.  At a summit between Chinese President Hu Jintao and Russian President Vladimir Putin earlier this year, the two leaders released a joint statement about their vision of international affairs in the future, criticizing the U.S. role in the world.

The Shanghai Cooperation Organization, a security group dominated by China and Russia, also recently called for a timetable for foreign -- that is, U.S. -- troops to be withdrawn from bases in Central Asia.

China has become the largest buyer of Russian military equipment. And last year, China and Russia signed an agreement settling all disputes along their shared border of more than 4,000 kilometers.

Trade between the two neighbors, which historically has been low, has also expanded.

Johannes Linn, an expert on global development at the Brookings Institution research group in Washington D.C., says Sino-Russian trade is expected to reach $80 billion by 2010.  "Russia, of course, provides mostly energy and raw materials, that is something that China much values and is very dependent on to a significant extent. Russia in turn gets a lot of mostly household items, such as apparel and furniture."

Despite growing Sino-Russian ties, analysts say many in Russia remain wary of their neighbor's growing economic and military might.

Yet given the large potential for friction between the two historic rivals, Dr. Linn sees closer Sino-Russian ties as good news for global stability. "Russia and China have a common interest in relations with each other that are aiming towards stable and, with each other certainly, peaceful coexistence, and given that these are two large countries, nuclear superpowers, I think it's in everybody's interest that these two countries have peaceful relations."

Many experts describe the China-Russia-United States relationship as a strategic triangle. Two of the three sometimes align themselves against the other. China and Russia might step up some of their anti-U.S. rhetoric, but most agree the United States will remain the dominant force in the triangle for years to come.