Yoshikazu Tsuno / AFP / Getty Images U.S. Vice President Joe Biden is greeted by Japanese officials upon his arrival at the Tokyo International Airport on Dec. 1, 2013

U.S. Vice President Joseph Biden Jr.’s trip to Asia was supposed to be about mutually beneficial trade partnerships, the tastiness of U.S. agricultural exports and a dose of good ol’ American love for a region that has been feeling a little neglected lately. Instead, his Asia excursion, which includes stops in Japan, China and South Korea, has been dominated by a regional security crisis that some fear could spark armed conflict involving the world’s three biggest economies.

In Tokyo on Dec. 3, Biden renewed American ties with the staunchest U.S. ally in Asia, amid concerns over Beijing’s creation last month of an air-defense identification zone that includes skies over disputed territory between Japan and China. The U.S. Vice President has joined Japan in rejecting the lines China has drawn in the sky, with Biden characterizing himself as “deeply concerned,” in an interview with the Asahi Shimbun, a Japanese daily. Biden and Japan’s conservative Prime Minister Shinzo Abe are scheduled to have a working dinner on Tuesday night. In the lead-up to Biden’s trip, U.S. officials reiterated Washington’s commitment to a longtime security alliance with Tokyo that calls for American troops to defend Japan in case of attack.

This wasn’t just idle talk. On Nov. 23, China announced the creation of an East China Sea Air Defense Identification Zone (ADIZ) that overlaps with previous aerial boundaries drawn by Japan and South Korea. The points of overlap are precisely where territorial disputes exist between China and its maritime neighbors, most contentiously over a scattering of islands in the East China Sea called the Senkaku in Japanese and Diaoyu in Chinese. (Taiwan is the third claimant to the bits of rock.)

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These uninhabited islets are administered by Japan but China makes historic claims to them, arguing that they were part of Japan’s imperial landgrab across Chinese territory. Japan argues they were terra nullius and therefore open to an extension of national sovereignty in the late 19th century. More recently, China also views the U.S. as complicit in the mess because the Americans reverted the specks of land to the Japanese in the early 1970s when the final stages of the U.S. occupation ended.

Tensions over the islets have intensified since the Japanese government nationalized three of them last year. Tokyo says it did so in order to keep an ultra-hawkish Japanese politician from buying them and turning them into a political trophy. But the Chinese government took the purchase as nationalist drumbeating by a former imperial power that Beijing says has not adequately apologized for its brutal occupation during World War II. Washington waded into the controversy by affirming that its security alliance with Japan included the Senkaku/Diaoyu Islands, even if the U.S. does not take an official position on who should own the disputed turf.

Now Beijing’s ADIZ is heightening tensions even further in East Asia. Any country can fashion its own ADIZ, a designation that carries no international legal weight and is different from national airspace. But China’s version uniquely carries an oblique threat of military action toward a foreign aircraft that passes through the contentious zone without giving flight information to the Chinese side. (Other ADIZs, by contrast, only require aircraft to notify a country if the planes are continuing on into that nation’s airspace, as opposed to merely passing through.)

Over the past week, South Korea, Japan and the U.S. have all flown military aircraft through the ADIZ without warning Beijing — in direct contravention of the rules China unilaterally set up last month. Tokyo and Seoul have also instructed their nations’ commercial airliners not to heed the Chinese demand for flight information. But American authorities have taken a different tack, advising U.S. airlines to inform Beijing of their coordinates in order to ensure their safety, while cautioning that they do not condone the creation of the zone itself. This U.S. stance has led the Japanese, in particular, to worry that the Chinese ADIZ is already attracting a modicum of legitimacy from the outside world.

Biden’s trip, which began on Monday in Tokyo and will then continue on to Beijing and Seoul, already had a component of fence-mending built into it. In October, amid the American debt standoff, U.S. President Barack Obama canceled a trip to Asia. (He is now expected to visit the region in April.) It thus falls on Obama’s loquacious Vice President to assure the continent that the U.S. takes it seriously, after more than a decade in which Washington’s attention has been preoccupied by the Middle East. A statement from the White House noted that Biden’s trip is designed to “underscore our commitment to rebalancing U.S. foreign policy towards the Asia-Pacific.” Some in the region, however, worry about the long-term U.S. commitment to that goal.

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The fraught situation in the East China Sea and other territorial disputes China has with neighbors in the South China Sea may force the U.S. to focus more intently on nurturing its ties with regional partners. Such a strategy, though, runs the risk of looking like a containment of China, a rising power whose economic and geopolitical heft has transformed the continent — and, indeed, the world — over the past decade.

The Obama Administration has repeatedly said its Asia rebalancing isn’t directed specifically at China. But few buy that, least of all Beijing. Meanwhile, other East Asian nations have been busy ramping up their military outlays, especially as China has taken a brawnier attitude toward the defense of turf in contested waters. Another development that shows the serious security situation in East Asia: this fall, both Japan and China formed new committees that resemble the U.S.’s National Security Council.

On Wednesday in Beijing, Biden is scheduled to meet Xi Jinping, China’s vigorous President who emerged with even greater clout after a key Communist Party conclave last month. Although the Americans don’t wish for the ADIZ issue to cloud the entire visit, Biden will surely be making his government’s dissatisfaction with the zone clear to the Chinese. At the same time, Xi will have to clarify to the U.S. why he signed off on the ADIZ last month. From the Chinese perspective, other Asian nations like Japan and South Korea have long carved out such patches of their own. Why shouldn’t Beijing do the same — and have its zone extend to what China believes is its territory, despite competing claims from Tokyo and Seoul?

“China needs to explain very clearly why we did this,” says Shen Dingli, a professor of international relations at the prestigious Fudan University in Shanghai, who has advised Chinese foreign policy makers. “This is specifically against the illegitimate action of Japan and the United States. Japan made its ADIZ in 1969 and included what is China’s territory [the Diaoyu/Senkaku Islands]. We tolerated this. Then last year, Japan nationalized the islands. We cannot tolerate it anymore. We warned that Japan should bear all the consequences for its actions, and the battle lines are now drawn.” Such steadfast opinions are hardly the exception in China, where mistrust of the Japanese runs deep.

Biden and Xi apparently enjoy a good rapport, stemming from the days when Xi was China’s Vice President and the American hosted his Chinese counterpart. “I would say [Biden] knows President Xi as well or better than probably any American, and possibly virtually any leader,” says a senior Obama Administration official. Given the chilliness in the air over lines drawn in the sky, a little show of warmth — between the Vice President of a superpower and the former Vice President of a rising one — may be just what is needed as winter looms.

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