So this move is aggressive and expansionist, in asserting a Chinese government right to know who is traveling in its (enlarged) vicinity. But some stories have suggested that it would lead to an immediate struggle or challenge over the right to fly, which it (probably) will not.

2) Why are the Chinese doing this? As a general proposition, this is of course one more sign of worsening relations between China and Japan, focused in this case on the tiny islands both countries claim to control. As for the immediate reasons for this move, no one outside the central leadership can say with any certainty, and perhaps not even anyone there.

The lines of authority and communication between civilian and military officials in China are murky in the best of circumstances. (Remember, the People's Liberation Army technically is commanded by the Chinese Communist Party, not the Chinese state.) The concept of a civilian commander-in-chief is not built into China's governing structure. Most people think that newish president Xi Jinping enjoys more support from the military than his predecessor—which most outsiders consider to be a good thing, since it reduces the chance of the military setting policy or creating new realities on its own.*

The ADIZ move is is a big enough step that Xi Jinping himself would presumably have been aware of it, and again-presumably would have thought it a worthwhile demonstration of Chinese "strength" and refusal to be pushed around. But for now that is guesswork rather than knowledge.

3) Is this likely to do China any good? The puzzling nature of Chinese foreign policy, especially its generally self-defeating "soft power" aspects, is a subject too vast for our purposes right now. In brief: the very steps that, from an internal Chinese-government perspective, are intended to make it seem confident, powerful, and attractive often have exactly the opposite effect on audiences outside China.

One famous illustration followed the world financial crisis of 2008. The Chinese economy recovered much more quickly than others; the U.S. looked like a house of cards; and the Chinese military made a number of expansionist-seeming moves in the South China Sea that quickly got the attention of neighboring countries. The result of this "over-reach" episode, as it is described now even in China, was to bring Japan, South Korea, Vietnam, the Philippines, Malaysia, and other countries into closer alignment with the U.S. than they had thought necessary before. By acting super-tough, the Chinese military made its real situation weaker.

This ADIZ case may become the next famous example. Whether it seems, either now or later, worthwhile from the Chinese leadership's perspective I have no idea. But at least in the short term, it appears to have alarmed the South Koreans, with whom Chinese relations had been steadily warming, plus introducing new friction into China's most important relationship, which is with the United States.