ON NOV 23, China declared an East China Sea air defence identification zone (Adiz).

Such air buffer zones are commonplace, so countries can set rules on aircraft in international airspace as they near their sovereign airspace.

But China's insistence that its rules - such as requiring aircraft to submit flight plans - apply to aircraft flying in the area, not just those that want to enter China's airspace, created alarm throughout the region.

So did its warning that "defensive emergency measures" would be adopted to respond to aircraft that refuse to follow the instructions. After all, the zone overlaps the existing Adiz of Japan, South Korea and Taiwan.

On Tuesday, the United States sent two unarmed military planes flying through China's Adiz.

Is the US action escalating tension in the region?

What might account for China's action of declaring an Adiz in the East China Sea?

How does this fit in with new Chinese leader Xi Jinping's foreign policy?

This snapshot of views from different sources attempts answers.

IS THE US ESCALATING TENSION WITH CHINA BY SENDING TWO PLANES THROUGH CHINA'S ADIZ?

• By Sam LaGrone and Dave Majumdar. They are respectively the editor of United States Naval Institute News and a long-time defence writer.
  
  

IT IS important to note that the zones are over international waters and the legalities that govern them are murky at best.

For example, Japan's Adiz encompasses its economic exclusion zone and also overlaps Taiwan's Adiz - which has caused tensions in the past.

The Adiz airspace is not "claimed" by whichever party is trying to enforce the zone. All a nation or party in question can do is ask for the identification, location and try to claim air traffic control of civil aircraft - and back the claim up with the threat of interception.

But the exact legal mechanism under international law is murky. The US government, for example, enforces its zones under legal theory that a nation has the right to set the conditions of entry into its territory.

"International law does not prohibit nations from establishing air defence identification zones (Adiz) in the international airspace adjacent to their territorial airspace," (according to) the US Navy's Commander's Handbook On The Law of Naval Operations.

"The legal basis for Adiz regulations is the right of a nation to establish reasonable conditions of entry into its territory. Accordingly, an aircraft approaching national airspace can be required to identify itself while in international airspace as a condition of entry approval."

Of note for this particular (instance), ignoring the Chinese Adiz is standard procedure for the US government.

"The United States does not recognise the right of a coastal nation to apply its Adiz procedures to foreign aircraft not intending to enter national airspace nor does the United States apply its Adiz procedures to foreign aircraft not intending to enter US airspace," the handbook states.

"Accordingly, US military aircraft not intending to enter national airspace should not identify themselves or otherwise comply with Adiz procedures established by other nations, unless the United States has specifically agreed to do so."

WHAT DOES CHINA WANT?

• This is an extract from an editorial in the state-run Global Times newspaper on Tuesday which has China calling on Japan to enter into negotiations for a peaceful East China Sea.
  
  

THE Chinese anticipated Washington would show support for Tokyo, at least in its declaration, and we predict that it will further pressure China with escalated tensions over the Diaoyu Islands.

However, the US' tough stance might turn out to become a catalyst for Japan to take further provocative actions against China on the East China Sea, instead of serving as a condition to prompt Beijing to alter its will and determination in establishing the Adiz...

It must be pointed out that Beijing set up the Adiz with an aim to avoid friction and conflicts. More than 20 countries have created their air defence identification zones and, in particular, Japan's Adiz has crossed the so-called "median line" in the East China Sea reaching only 130km from China's mainland. Therefore it is indispensable for Beijing to include the Diaoyu Islands in the new Adiz.

If Tokyo desires a peaceful East China Sea, it is supposed to negotiate with Beijing on the operation of both air defence zones and effectively manage and control crises, which is not difficult with advanced technologies.

However, Beijing cannot influence Japan's decision if it takes "unexpected" actions against China's aircraft in the Adiz.

We are convinced that the People's Liberation Army must have taken into account the worst situation when a military mishap breaks out.

If Washington attempts to interfere in this Sino-Japanese territorial row, China is willing to keep it company to the end.

HOW DOES CHINA'S MOVE FIT IN WITH NEW PRESIDENT XI JINPING'S EMERGING FOREIGN POLICY AND MILITARY STRATEGY?

• By Nicholas Szechenyi, Victor Cha, Bonnie S. Glaser, Michael J. Green, Christopher K. Johnson, Centre for Strategic Studies and International Studies.
  
  

AT first glance, the establishment of the Adiz seems to be at odds with the Xi administration's incipient foreign policy vision.

Since coming to power, the new leadership has seemed to focus its energies on rebooting Beijing's relations with its regional neighbours. China has sought to calm tensions with Asean over territorial disputes in the South China Sea by adopting, at least rhetorically, a more constructive approach towards managing the problem through dialogue aimed at an eventual agreement on a code of conduct.

Mr Xi and his Premier, Mr Li Keqiang, stepped up the charm offensive with their respective performances at last month's Asia-Pacific Economic Cooperation and East Asia Summit meetings, signing deals worth billions in an economic blitzkreig reminiscent of Beijing's highly effective "smile diplomacy" that began in the late 1990s. Mr Xi and his colleagues seemed to cap off this new approach by holding a rare internal policy conclave in late October focusing on strategies for further improving China's relations with peripheral states.

Of course, one can make the argument that relations with Japan are a special case and that Beijing's actions are consistent with a long-standing tradition of seeking to avoid tensions on multiple fronts at any one time.

Viewed through that prism, the friendlier approach towards Southeast Asia can be characterised as a necessary precursor to an even tougher policy approach towards Japan.

But it would be a mistake to confine the import of the Adiz solely to Beijing's cat-and-mouse game with Tokyo. Instead, it should be understood within the context of the new leadership's framing of the security challenges it faces in the region.

Distracted by its once-in-a-decade leadership transition and a struggling economy, the senior Chinese leadership last year largely deferred an authoritative review of the implications of the US strategic rebalancing towards Asia for China's security.

With the succession now complete, however, the outlines of Mr Xi Jinping's assessment of the situation are coming into sharper focus.

Recent authoritative Chinese documents, such as this year's defence white paper, have affirmed the continuing validity of China's primary external strategic guideline (in) its judgment that China has a "period of strategic opportunity" extending through 2020 in which a benign external security environment allows it to focus on its internal development.

That said, these writings also suggest that the "period of strategic opportunity" is under "unprecedented stress" and that the US rebalance is the source of that stress.

Against that backdrop, Mr Xi's frequent admonitions to the People's Liberation Army (PLA) to be prepared to "fight and win wars" take on added significance.

Along with hints from the just-concluded Third Plenum that the leadership is considering sweeping military structural reforms aimed at improving the PLA's combat effectiveness, it leaves an impression that the leadership is signalling that it judges the risk of conflict in the region to be on the rise.

The establishment of the Adiz can therefore be seen as contributing to the seeming sense of urgency that Mr Xi is seeking to foster in shaping the regime's response to this threat assessment.

It also suggests that, while still the predominant concern, the possibility of an accident in the disputed Senkaku/Diaoyu territory is not the only risk of escalation in the East China Sea that US security planners should be focusing on.