The world’s condemnation of Vladimir Putin’s power grab in Ukraine is missing one important voice: China’s. That’s no surprise.

Since assuming office, Chinese President Xi Jinping has put great emphasis on building up his relationship with Russian President Vladimir Putin. Both men fancy themselves strong, charismatic leaders bent on restoring their nations to greatness.

But if China wants to be the world leader it claims to be, it cannot afford to sit on the sidelines this time. Xi spoke with President Barack Obama on Sunday night and, contrary to Russian claims of Chinese support, agreed on the "importance of upholding principles of sovereignty and territorial integrity, both in the context of Ukraine and also for the broader functioning of the international system."

That’s a nod in the right direction, not a bold step.

The difficulty for Xi is that he considers Russia -- his first overseas stop after becoming president -- to be a useful counterbalance to the West. It’s also an increasingly important source of energy and advanced weaponry.

Even as China, in its one public comment on Russia’s incursion in Crimea, reaffirmed its respect for Ukraine’s independence and sovereignty, it underscored that "there are reasons that the Ukrainian situation is what it is today" -- a reference to the messy collapse of the Soviet Union, which both Xi and Putin agree was a tragedy.

Yet the real bond in the Sino-Russian relationship is the very principle Putin has just violated in Ukraine: noninterference in another nation’s internal affairs. Moscow and Beijing cling tightly to the dictum to justify United Nations Security Council vetoes. It’s critical to both, given their shared worries about how outsiders might exploit ethnic tensions and democracy movements within their countries.

If Putin continues to advance in Ukraine, forcing a military confrontation or breakup of the country, he may well push China to take a stronger stand. The truth is that in material terms, China gains less than Russia does from their relationship. The latter accounts for a little more than 2 percent of China’s external trade. While volumes are growing, in 2011 China got only about 6 percent of its imported oil from Russia.

And though China is Russia’s largest trading partner, Putin has also been hedging his bets. He has sought to expand rail links, pipelines and energy exports not just to China but also to both Koreas and to China’s archrival Japan. Russia is aiming to sell sophisticated weaponry to India, and has deepened economic and military relations with Vietnam. Moscow has longstanding fears about Beijing’s influence in its Far East, where an influx of Chinese traders has virtually colonized the region.

In other matters affecting international stability, China has acknowledged its responsibility to get involved. It has, for instance, agreed to chase pirates off the coast of Somalia even if they flee into territorial waters, and it has chosen not to obstruct some international sanctions against Iran and North Korea. Implicitly tolerating Putin’s adventurism now only reinforces fears about China’s behavior -- especially among its neighbors, who already suspect that it aims to annex several islands and atolls across the East and South China Seas.

China ultimately shares the same goals in Ukraine as the rest of the world: to affirm the sanctity of international borders, avoid bloodshed and restore stability to global markets as quickly as possible. All would be accomplished much faster and more durably if China spoke out now against Putin’s aggression.

~Bloomberg News