Chinese map of its new Air Defense Identification Zone, from Xinhua.

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.

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. 

Which leads us to ... 

4) So what about the U.S. reaction, including the bombers? The worsening Japan-China struggles are, for the United States, the opposite of the cynical view of the 1980s Iran-Iraq war. Back then, as the wisecrack held, the U.S. wished both sides could lose. This time, the U.S. would prefer that both sides win—or, more precisely, that they not fight. A struggle between the two, especially over the contested tiny islands, puts the U.S. in a lose-lose predicament. Public mood and government policy in each country is increasingly hostile to the other—but we're deeply connected to both of them, plus we have a treaty obligation to defend Japan against attack. We want this fight to go away, without our being forced to take a side.

Why risk getting involved, plus angering the Chinese, by sending B-52s through the new ADIZ? I think the Pentagon's initial explanation is the right one—on the merits, and as a matter of public diplomacy. The United States is not taking sides in this Japan-China island dispute, but it is against either side unilaterally changing the status quo. Also, in continuing "routine training flights"—which is how the B-52 mission was described—it is underscoring the U.S. commitment to existing rules on access to international air space. It was mildly risky to send that flight, but it would have been riskier not to react at all.

5) How Can You Learn More. This will be all over the news, but a go-to site is that of Andrew Erickson, a defense expert who is fluent in Chinese and is providing a steady flow of documents and analyses from Chinese sources.

And then there are our friends at NMA in Taiwan. Of course they're critical of the P.R.C., but ... well, see for yourself.

* The most closely studied example of "creating new realities" was the Chinese test of an anti-satellite weapon in 2007, which left debris in the path of other satellites and was roundly criticized worldwide. Even now people debate who exactly gave the go-ahead for this move: someone inside the PLA, or the civilian leadership of then-president Hu Jintao.

We want to hear what you think about this article. Submit a letter to the editor or write to letters@theatlantic.com.