East Asia and the U.S. had better get used to this sort of thing. China's heavy-handed declaration of an unusually demanding air defense identification zone (ADIZ) is only one in a series of moves in which the country will gradually try to exert control over its maritime approaches. Worryingly, it may also be an early example of China's Communist Party contriving to raise international tension as a means of rallying popular support at home.

Just about everything encourages China to be more assertive in neighboring waters, from its mistrustful, sometimes hostile view of the outside world to its domestic politics, rising strength and growing nationalism—and, not least, Japan's refusal to face up to its atrocious pre-1945 behavior.

Commercial air services are running normally through the ADIZ, which covers much of the East China Sea, including islands and a reef disputed by China, Japan and South Korea. There is no disruption even of flights by Japanese airlines, which are refusing to supply the Chinese authorities with the demanded flight plans for the zone, while other countries' commercial carriers cooperate. U.S., Japanese and South Korean military flights, however, have ignored Beijing's demands.

“From now it is a question of enforcement,” says Rory Medcalf, a specialist on Asian maritime security at the Lowy Institute, a think tank in Sydney. Having now asserted its rights, how—or will—China compel other countries to fully recognize them?

Airline compliance can be enforced administratively simply by withdrawing landing rights, although there is no sign of that happening. If Beijing were to not let Japanese airlines go to China, Tokyo would surely respond likewise. There then would be no direct air services between the world's second- and third-largest economies.

Attempts at enforcing the rules on military flights would surely be dangerous. Chinese vessels sometimes collide with U.S. naval ships in China's exclusive economic zone (EEZ), trying to enforce a claimed right to exclude foreign military activity. But threatening behavior in the air can have tragic results, as shown in 2001 when a Chinese fighter pilot died after apparently flying too close to, and colliding with, a U.S. Navy EP-3 Orion intelligence aircraft.

Most media attention given to China's Nov. 23 declaration of the ADIZ has focused on ham-fisted Chinese diplomacy: ADIZs are common enough, but China made its declaration without consultation while in a tense confrontation with Japan over waters that the zone covered. (The zone also covers a reef disputed by China and South Korea, which now plans to extend its own ADIZ.) But in one respect the Chinese ADIZ is more proprietorial than is usual for such a zone: It demands flight plans for all aircraft entering it, regardless of whether they are flying to China. That is the destabilizing aspect of the move, says Gen. Martin Dempsey, chairman of the U.S. Joint Chiefs of Staff.

It is also reminiscent of the attempt at enlarging the meaning of the EEZ. Both steps are part of a strategy that Sydney University's John Lee calls China's salami-slicing—with each move, China seeks to take another slice of authority over nearby waters. Other examples are progressive attempts at enforcing the economic rights of the EEZ claim in the South China Sea.

The East China Sea ADIZ “is a strategically clever move because it has forced other countries to accept China's authority and gives a pretext to escalate” in a future crisis, says Medcalf. Crews of foreign airliners passing through the zone but not on their way to China are, in effect, doffing their caps at Beijing as they report flight plans and maintain the required radio contact.

In the U.S. on Dec. 3, Rep. Randy Forbes (R-Va.), chairman of the House Armed Services seapower and projection forces subcommittee, wrote to National Security Adviser Susan Rice asking the administration to reassess the FAA's recommendation that U.S. airlines follow China's new rules. “By advising U.S. airlines to comply with China's ADIZ, the administration is legitimizing Beijing's attempt to subvert international airspace at the same time it is also, rightfully, condemning such a move,” Forbes wrote.

From the outside, China's actions look simply aggressive, especially when its forces take such action as illuminating Japanese warships with fire-control radars. But from China's point of view, controlling nearby waters creates a defensive buffer, says Li Mingjiang, a specialist on Chinese foreign policy at Nanyang Technical University in Singapore. The purported EEZ rights are key: If China can get other countries to accept its ownership of the many disputed islets, rocks and shoals stretching from near South Korea to near Indonesia, and if it can enforce a rule that foreign warships and warplanes may enter the resulting enormous EEZ only with its permission, then it will feel a lot safer. The buffer is not yet built, so the salami-slicing will continue until it is, or until China is somehow persuaded to stop.

But why should China feel that it needs such a colossal security buffer? After all, other countries do not feel a need to keep foreign forces at a distance of hundreds of kilometers. The answer is that China still has the “us-and-them” mentality familiar in the West before World War I. “China perceives itself and is probably perceived by the West as an outsider in the international system,” says Li. The country has few real friends except Pakistan and North Korea, the latter also part of its strategic buffer. Ordinary Chinese speak quite easily of the possibility of war, especially with Japan.

Many of them are also confused by the willingness of the West to tolerate what the British military historian Max Hastings has called Japan's “collective rejection of historical fact,” the millions of deaths it caused in 1937-45, mostly in China. It would be as if Russia were expected to live with a Germany unrepentant for its wartime atrocities and remembering little about them.

Li points out that China sees its buffer being resisted, and its security undermined, every time the U.S. works to bring down the North Korean regime, preserve the independence of Taiwan (effectively, the biggest disputed island), and back Japan and Southeast Asian countries against Chinese territorial bullying.

Domestic politics may be playing a part in the current dispute—or they may next time. China's foreign policy is tough not just because authoritarian rulers like it that way. The Chinese people, pumped up on partly manufactured nationalism, generally want their country to throw its weight around even more. Any sign of weakness in foreign affairs attracts widespread criticism.

For years it has been commonly said that the party relies on fast economic growth and nationalism to stay in power. That has raised concern about what the rulers may do to heighten nationalism when the economy slows—which it is doing now. At the same time, the party is under pressure from a populace that, thanks to the Internet, finds it ever easier to share grievances over everything from pollution to corruption and, coming soon, likely disruptive economic reforms planned by the new administration of President Xi Jinping.

“It is quite difficult for the Chinese government even to appear to be weak,” says Li. “And the new leadership understands the usefulness of using external crises to unite the domestic population to position themselves politically to push for reforms and their domestic program in China.”

This heightens the danger. First, there is a clear temptation to create a crisis, and that temptation will rise if and when the party's position weakens. Second, if China takes a step too far in setting up its buffer, it may be unable to step back.

With Michael Bruno and Michael Fabey in Washington and Adrian Schofield in Wellington, New Zealand.