Why Is the U.S. Rehearsing for a Chinese Invasion of Japan? When the U.S. Navy's 60,000-strong Seventh Fleet joined with the Japanese military last month to simulate "re-invading" part of Japan that had been taken by an outside force, the hypothetical invader went un-named for reasons of diplomatic decorum. But that didn't stop a senior Japanese military official from boasting to a national newspaper, "We'll show China that Japan has the will and the capability to defend the Nansei Islands. [The exercises] will serve as a deterrent." Even if he had said nothing, everyone involved understood that the U.S. and Japan were rehearsing a counter-attack against a possible Chinese invasion of Japan. Since then, an unrelated and seemingly minor dispute over a Chinese trawler captain arrested in Japanese waters has spiraled into a heated, ongoing standoff between leaders of both nations. Japan refuses the release the fisherman, despite China suspending all relations between its officials and Japan's--often a prelude to war--and threatening "strong countermeasures." Is China's invasion of Japan nigh? Is it only a matter of time? "No one's worried about China invading Japan," Abe Denmark, an expert with the Center for New American Security on U.S. security policy in East Asia, assured me. "This is about a long-standing disagreement between China and Japan that flares up occassionally. And it's flared up recently." In other words, this kind of tension is more or less routine for Sino-Japanese relations, and it's not leading to war anytime soon. But China's increasingly aggressive foreign policy and the volatility of China's relationship with Japan--not to mention with the rest of its East Asia neighbors--is a very real concern for the U.S. The recent U.S.-Japan military exercises were just one part of a concerted effort to entrench U.S. military influence in East Asia and bring long-term stability to a rapidly changing and often contentious part of the world. Someday in the future, our influence abroad, and in East Asia especially, will wane. The Obama administration wants to guide East Asian politics in a direction that will be most beneficial to long-term American interests. The more time that the U.S. spends working with foreign militaries such as Japan's, the more those militaries, and thus the nation they represent, institutionalize dependence on the U.S. Japan is willing to go along with this because it sends a message to potential enemies--especially China--that an attack on Japan would also be an attack on the U.S. Regular U.S.-South Korea joint military exercises, most recently in July, have the same effect. The exercises strengthen communication and coordination between our military and theirs, making us better partners should war arrive and increasing the deterrence effect. They also help justify our enormous military presence on their soil--something that has been politically controversial in Japan. And they reinforce a tradition of cooperation in which the people and politicians of Japan, South Korea, etc., see the U.S.--not China--as their natural, cultural ally. That kind of trust can last a long time. Trust and cooperation are hard to find among the nations of East Asia, which never quite established a European-style practice of collectivity. Nowhere is the inability to resolve minor disputes--and the frightening potential for those skirmishes to escalate uncontrollably--more apparent than across the region's countless tiny islands. To put it simply, no one knows whom they belong to but everybody wants them. As China and Southeast Asia industrialize, islands and their resources are becoming more desirable. "A lot of this is a remnant from periods of instability in East Asia's past," Denmark told me. "Over the years, different countries have controlled different islands." Competing claims have led to many inflammatory incidents such as Japan's arrest of the Chinese fisherman and naval skirmishes between China and Thailand. There are a handful of ways to determine ownership, but some of them are contradictory, and political leaders often have more faith in military confrontation than lobbying the United Nations. Enter Secretary of State Hillary Clinton, who in July worked hard to peacefully resolve an island dispute between China and Thailand. The U.S. interest here is four-fold: establish a mechanism for peaceful conflict resolution, so that war is less likely; build precedent for the rule of international law, so that China can't simply use its navy to bully its neighbors; keep the U.S. involved in East Asian politics so we aren't shut out; and prevent China from dominating the South China Sea. The oil-rich sea lane has become a strategically crucial link from East Asia to the Indian subcontinent, the Middle East, Africa, and beyond. Those connections are rapidly becoming some of the most important and most heavily trafficked trade routes of the global economy. Whoever controls the South China Sea will also control the ability of navies--whether Chinese, American, Indian, or NATO--to project force across the Eastern and Western hemispheres. But why should all of this matter so much to the U.S.? After all, our military is many times stronger than China's and we still control most of the Earth's seas and skies. The word that many scholars use when talking about long-term U.S.-Sino relations is "multi-polar," which reflects the growing belief that China will one day join the U.S. as the world's second superpower, fundamentally reshaping a world currently defined by American dominance. The question isn't will China rise, it's what happens when it does. If we simply let current trends continue, it's entirely foreseeable that China could cajole, persuade, or bully the rest of East Asia under its influence. The U.S. can handle Chinese competition, but a unified East Asia could undermine the U.S. in any number of ways. Limiting our freedom of movement in the Pacific and Indian oceans would only be the beginning. Another risk of inaction could be regional war. As China expresses more dominance over its neighbors, if regional diplomatic institutions remain too weak to ensure peaceful conflict resolution, it's possible that China could come to blows with states such as Thailand or, yes, Japan. War is always terrible, but the modern military conflicts of East Asia have been especially brutal, costly, and destabilizing. If a regional war broke out, the U.S. would have nothing but bad options--enter into war against China? cut off economic ties? sit it out and watch the rest of Asia cower to Chinese dominance?--all of which would spell disaster for long-term American interests. There's little question that China will eventually join us as a world superpower. Rather than fighting the inevitable or pretending it isn't so, Clinton's State Department is laying the groundwork for a mutlipolar world that is as beneficial and acceptable to the U.S. as possible. That includes reinforcing East Asian multilateral institutions, rehearsing regional avenues of conflict resolution, and entrenching U.S. military cooperation with China's neighbors. Strange though it may seem, sometimes the best way to promote peace is by practicing war. Image: U.S, Thai, and South Korean marines pose for a photo during joint military exercises in Thailand. The annual war games, Cobra Gold 2010, involve 14,000 military personnel from six nations: the U.S., Japan, Thailand, South Korea, Singapore, and Indonesia. Can you spot who's missing? Photo by Pornchai Kittiwongsakul/AFP/Getty.