This is a strange development—China's establishment over the weekend of an ADIZ, or Air Defense Identification Zone, in an expanded area of the East China Sea, eliciting alarmed reactions from Japan, the United States (which today sent two B-52s through the zone), South Korea, and other countries in the region. A few points to bear in mind as you follow the story:
1) What is an ADIZ, anyway? Many news stories have presented the ADIZ as if it were comparable to a no-fly zone, or an extension of territorial sovereignty. It's not quite that. All four words in its full title are important, including the least obvious third one: Air Defense Identification Zone. The idea is to create an area where the relevant authorities have a right to know who is flying, and where they are going. It doesn't necessarily mean that flights are going to be challenged or interfered with.
For reference, here is the way the ADIZs around the continental United States look:
In practice the U.S. zones mean that aircraft entering ADIZ space—most of the time, those bound for U.S. cities from other countries—must have filed flight plans and been cleared along their routes by Air Traffic Control. Virtually all of the world's airline flights operate on filed-and-cleared flight plans anyway, so the ADIZ makes no practical difference in airline operations. (The Chinese have said the same will apply in their new zone.) You can get extremely detailed info from the pertinent FAA regulations. They include this definition:
Air defense identification zone [ADIZ] means an area of airspace over land or water in which the ready identification, location, and control of civil aircraft is required in the interest of national security.
"Control" in this sense means subject to the directions of an Air Traffic Controller—"turn right, heading 270"—rather than something more forceful.