The international outcry over Beijing's abrupt establishment last November of an air-defense identification zone (ADIZ) over the East China Sea has finally calmed down. China's unilateral move was sensational because it proclaimed its jurisdiction over the ADIZ by stating it would take coercive measures against foreign aircraft that did not comply with its demands.

China's establishment of the ADIZ also heightened the sense of crisis — given that the ADIZ challenges Japan's claim to the Senkaku Islands — that has grown since Chinese maritime law-enforcement vessels began making provocative passages through the zone more than a year ago.

In the age of jet aircraft, an ADIZ is simply a temporal buffer for identifying friends and foes and, if necessary, for scrambling interceptors to defend territorial airspace. Many countries don't try to proclaim one unless they're sure it will be recognized internationally as being legal. During the Cold War, there was a West German ADIZ established in East German airspace, and today's South Korean ADIZ extends to the southern one-third of North Korean airspace.