China's surprise declaration of a discretionary air reporting zone over the East China Sea caught the region unawares.
There was neither any warning nor consultation on its plans. More troubling was that precisely what China would choose to do to enforce implied restrictions was left more than a little vague, because there has been no normative behaviour demonstrated although defensive air zones have a history going back 60 years.
The American B-52 planes' fly-past, which drew no response, looked to most observers like a calculated dare, but was most likely intended to reassure US security allies Japan and South Korea.
To Beijing's way of thinking, keeping its intent open-ended has the same effect as deterrence - whether against military intelligence gathering or to prevent territorial encroachments. The latter is suspected be the main motivation for the decision.
Japan's Abe government has rallied opposition to the zone, reaction to which has been uniformly negative. China has regarded these objections as inevitable and irrelevant, asserting its rights to a zone that others also have.
This delicate new reality in North Asia was underlined in US Vice-President Joe Biden's visit which took in all three nations whose designated air zones intersect. He did not ask that China rescind its decision, which Japan had dearly wanted.
How could he credibly do so, just as he was heading to meet the Chinese leaders in Beijing?
The United States was the originator of far-reaching airspace requirements. Japan has had long-standing protections. Korea has extended its airspace in protest.
What is left for the world to hope for is that Chinese enforcement will be circumspect, to avoid incidents and an impression of unwarranted airspace overlordship.
All of Asia now waits to see what China might do next to complete a cordon sanitaire. If zones are declared over the South China Sea and the Yellow Sea, where territory is also contested, ASEAN would wonder about China's good faith in negotiating a code of conduct to regulate disputes.
Mr Biden was forthright in reminding China of unintended consequences and miscalculations over military and civilian aircraft movements.
These recent developments have made East Asia a more dangerous place. China and Japan both bear responsibility for this, as well as for managing their testy ties.
Like it or not, their fortunes and futures are inextricably linked. If both Japanese Prime Minister Shinzo Abe and Chinese President Xi Jinping - The Straits Times' choice for joint winners of this year's ST Asian of the Year award - are able to steer a steady course in their relations, they will help bring new prosperity to millions around the region.
If they fail, disaster looms.
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