If China were a U.S. congressman, it would be Tweeting threatening pictures of its biceps to its rivals.

Beijing recently warned Vietnam and the Philippines not to explore for oil in disputed waters that China claims, and late last month Chinese naval patrol craft allegedly cut the surveying cable of a Vietnamese seismic research boat. Manila's recent grievances against China are similarly severe. The Philippine government claims that China has harassed its exploration vessels, illegally unloaded supplies to build an oil rig in disputed waters and sent fighter jets into its airspace.

Apparently, half a year or so of good behavior in Asian waters is too much of a burden for China's leaders. After various provocations in the East and South China Seas culminated in a very public criticism by U.S. Secretary of State Hillary Clinton at the Association of Southeast Asian Nations Regional Forum last year, Beijing tamped down its behavior and tried to return to the smile diplomacy that had won it so much ground in recent years. Now such patience has worn thin, and China is back to threatening its neighbors.

While Beijing claims that Hanoi and Manila broke agreements on joint exploration, the world should be worried that China feels no qualms about using its growing military power to resolve disputes to its satisfaction. As its national power and military capabilities increase, it seems less willing to concede any of its expansive maritime claims.

Beijing has been testing Washington's resolve for the past decade, just announcing live-fire exercises to be held somewhere in the western Pacific, undoubtedly close to U.S. and Japanese installations. As a direct result of Beijing's recent actions, Hanoi has announced its own live-fire naval drills off its central coast. To provoke such behavior is to contribute to growing instability, no matter how limited such actions may seem.

Asian nations and the United States have yet to figure out how to respond to China's assertiveness against peaceful neighbors. Getting the response right is important for at least three reasons.

First and most importantly, China is, whether by design or not, creating the conditions under which its neighbors feel no choice but to conform to its demands regardless of their own national interests. If such behavior becomes the norm, then China will have significantly, perhaps fundamentally, changed the nature of Asian regional politics.

This will provide it with unlimited leeway to make other demands, some of which may seem fanciful now, such as vetoing maritime development plans or interfering with freedom of navigation. Once such a tipping point is reached, it will be difficult if not impossible to easily return to more cooperative multilateral patterns of behavior.

Second, the more that China gets away with intimidating or interfering with its neighbors, the more other disruptive regimes, such as North Korea's, will be emboldened to do the same. The result is to increase the slow destabilization of the region and to make it much harder for liberal nations to agree to play by international rules. This will further put pressure on the U.S. to maintain its role as a credible defender of stability at a time when its own resources are becoming more stretched.

Finally, as Vietnam's response to China's bullying shows, smaller nations may not always take such intimidation lying down. The potential of saber-rattling and even clashes will increase, as U.S. Secretary of Defense Robert Gates warned this month at the Shangri-La Dialogue in Singapore.

China's actions already are resulting in an arms race in the broader Indo-Pacific region. Orders of naval equipment have increased dramatically in recent years. India alone plans on spending over $50 billion to strengthen its navy, while Japan is bolstering its submarine fleet and building a helicopter carrier big enough to launch airplanes.

All this makes the American role more important even as it becomes more difficult. Distrust and fear of China notwithstanding, few Asian nations yet want to be seen as balancing against China on the side of the U.S. Many of Washington's allies are also forecasting flat or declining overall defense budgets in the future.

In short, unless the U.S. is willing to trust that everything will turn out fine, it has no choice other than to keep up its current security commitments and to maintain support for standards of reasonable behavior, even as it continues to engage China.

The global economy, including China's, depends on a stable and growing Asia. Yet the trends of recent years call into question assumptions about Asia's peaceful future. The waters of this continent are becoming more turbulent, though undercurrents hide much of the change. A region that has seen extraordinary economic growth over the past half-century now fears uncertainty and worse. If China wants to be respected as a great power, it will have to learn to curb its demands—and its temper.