More lines were drawn in the East China Sea (or rather in the skies above it).  With very little notice, China declared a sweeping air defense identification zone (ADIZ) over much of the East China Sea as of November 23 at 10:00 a.m. (local time).  Countries typically use such zones to expand their early warning against potential airborne threats.  Aircraft that fly within those zones are required to file flight plans and identify themselves to the appropriate authorities; otherwise those authorities may dispatch combat aircraft to intercept them.  China’s new ADIZ covers an area that contains two disputed maritime territories.  The first consists of islands, called Diaoyu in China and Senkaku in Japan, that are claimed by both Beijing and Tokyo.  The second is a small submerged rock, called Suyan in China and Ieodo in South Korea, which is claimed by both Beijing and Seoul.  South Korea has operated a small research station there for the last decade.  Shortly after China’s new ADIZ went into effect, its air force mounted its first patrol of the area; Japan spotted a Y-8 maritime patrol aircraft and a Tu-154 electronic intelligence aircraft over the East China Sea.

China’s demarcation follows a widely-publicized 18-day Japanese military exercise across southern Japan.  The exercise was one of an annual series that is normally held in November.  In 2011, a similar exercise was held that involved 35,000 Japanese personnel and the U.S. aircraft carrier George Washington.  After tensions were ratcheted up between China and Japan over the disputed Senkaku Islands in September 2012, Tokyo shelved that year’s exercise.  This year’s iteration involved 34,000 military personnel, six ships, and 360 aircraft.  The exercise featured air defense missile battery drills on Okinawa as well as an amphibious landing, supported by a Japanese helicopter carrier, on the uninhabited atoll of Okidaitōjima, about 250 miles southeast of Okinawa.

China’s new ADIZ requires aircraft operating within the zone to register flight plan, radio, transponder, and logo information with its Civil Aviation Administration.  But the Ministry of National Defense is the “administrative organ” responsible for the zone.  Aircraft that violate the rules of the ADIZ could prompt the Chinese air force to adopt “emergency measures.”  Japan maintains a similar zone around its nearby islands.

Certainly China’s action has reverberated across the Asia-Pacific.  As one South Korean official noted, the focus of South Korea’s upcoming talks with China will likely shift from strengthening trust and cooperation to the ADIZ controversy.  Even Australia summoned the Chinese ambassador in Canberra to express its concern.  But those that could ultimately end up facing a similar situation might be the countries of Southeast Asia.  In announcing the ADIZ, the Chinese Ministry of National Defense referred to its authority over “the area enclosed by China’s outer limit of the territorial sea.”  Of course, there is another “territorial sea” that China claims—the South China Sea.  Within that sea, China has many other maritime disputes.  The most recently visible one is between China and the Philippines over Scarborough Shoal, which led Manila to challenge China’s maritime claims before a United Nations tribunal earlier this year.  There are also the long-running disputes between China and Vietnam over the Paracel Islands as well as among China, Brunei, Malaysia, the Philippines, and Vietnam over the Spratly Islands.  But by mentioning the “outer limit of the territorial sea” China also revives a long-dormant dispute between it and Indonesia over the waters along the northern edge of Indonesia’s Natuna Islands, which have offshore natural gas fields.  China’s use of an ADIZ to strengthen its sovereignty claims in the East China Sea suggests that it might try a similar approach in the South China Sea too.  China’s Ministry of National Defense spokesman, Colonel Yang Yujun, failed to dispel such notions when he said that China would establish additional zones “at the right moment after necessary preparations are completed.”

More practically dangerous for the United States is that China’s ADIZ creates a situation in which American reconnaissance aircraft, which regularly patrol the East China Sea, may increasingly encounter Chinese fighter jets.  (Such patrols have long annoyed China.)  To appreciate the danger, one needs only to recall the April 2001 incident when a Chinese J-8 fighter jet collided with a U.S. Navy EP-3 reconnaissance aircraft over the South China Sea.  The EP-3 was forced to land on China’s Hainan Island where it was interned, triggering a two-week long crisis between China and the United States.

Little surprise, then, that China’s demarcation drew an immediate response from the United States.  Secretary of State John Kerry commented that he was “deeply concerned” and that China’s “unilateral action constitutes an attempt to change the status quo in the East China Sea”; Secretary of Defense Chuck Hagel flatly stated that the United States would not recognize China’s control over the zone.  To make that point clear, the United States ordered two B-52 bombers to make an unannounced transit of the East China Sea on November 26.  No doubt, Washington also wanted to set a precedent for American combat aircraft to operate within the zone without notifying Chinese authorities.

Tokyo took an equally stern tone.  Prime Minister Shinzō Abe said that Japan would not recognize the zone.  He even persuaded Japan’s major airlines not to file flight plans with Chinese authorities on routes through the East China Sea.  Both Japan and South Korea flew military aircraft into the zone on November 27.  Soon after, China announced that it sent more aircraft to patrol the area, including a KJ-2000 early-warning aircraft and several J-11 and Su-30 fighters.

Most likely, China is trying to use the ADIZ to not only respond to Japan’s recent military exercise, but also enhance its sovereignty claims to the East China Sea (and the islands within it).  Earlier, it began maritime law enforcement patrols in the area to do the same.  Hopefully, China understands that it is setting the stage for future conflict if it pushes its claims too hard.  Already, China has chipped away at the credibility of its own diplomatic charm offensive in Southeast Asia, which Beijing just launched at the Asia-Pacific Economic Cooperation forum in October.  Even Southeast Asian countries with less-apprehensive views of China, like Indonesia and Malaysia, cannot help but take notice.

China’s establishment of its air defense information zone in the East China Sea raises another question: why take such a step now?  Is it because China feels the need to immediately respond to Japan’s recent military exercise; or because Beijing knows that the world’s attention is focused on the successful international negotiations in Geneva over Iran’s nuclear program rather than its actions in the East China Sea; or because China sees the Obama administration’s commitment to its Asian allies as fundamentally weak (and wants to test it)?  Thankfully, Beijing decided to declare its ADIZ after Japan concluded its military exercise.  At least, there will be a full year before Japan conducts its next set of military drills in the area.