To read the seismic signal sent from an abandoned coal mine in the mountains of North Korea's coast, you must first recognize that it represents four major failures, two grave dangers, and one big opportunity.

The apparent explosion of a nuclear device, coming after two decades of trying to stop North Korea from achieving this goal, is a manifest failure of policy on four fronts -- a failure of U.S. nuclear non-proliferation policy, a failure of international diplomacy, a failure of Chinese leadership and a failure of South Korea's strategy of engaging the North.

Having failed so completely, the world now faces two grave dangers. The first is the very real threat of war on the Korean Peninsula, triggered by a series of escalatory actions in the wake of the bomb test. The second is the danger that North Korea will proliferate its nuclear technology, materials or know-how to others -- not the least to another nuclear hopeful, Iran.

But there remains a lone and tenuous opportunity. Having removed all ambiguity about its nuclear ambitions, North Korea may finally have created a common sense of threat that will galvanize the kind of concerted international action that so far has been absent.

THE FOUR FAILURES

Non-proliferation failure

The United States has spent two decades trying to stop North Korea from going nuclear, a turbulent period of crisis and negotiation that even went to the brink of war. At least three administrations confronted this problem and none, certainly not the Bush administration, can escape blame.

North Korea agreed to sign the Nuclear Non-Proliferation Treaty (NPT) in 1985, but it stalled before signing an agreement with the International Atomic Energy Agency (IAEA) in 1992 to place its nuclear facilities under international safeguards and inspections. During that time the North Koreans reprocessed some spent fuel from their reactor into plutonium - an amount that American intelligence believes was enough for building one or two warheads.

North Korea's resistance to full inspections, while it kept pulling spent fuel rods out of its reactor, provoked a crisis in 1994 and led the Clinton administration to ready military forces to strike the North's nuclear facilities. In a last-minute deal, North Korea froze its reactor and reprocessing facilities, effectively halting plutonium production under IAEA supervision. In exchange, the United States, Japan, South Korea and others agreed to construct two light-water reactors for North Korea and to supply fuel oil until the reactors came online.

The deal was troubled from the start. Neither party was satisfied with the compromise or the way it was to be implemented. By the late 1990s, the North had begun a secret effort to acquire uranium-enrichment technology from Pakistan and, in 1998, tested a long-range ballistic missile. Despite this, the plutonium freeze remained in place. But it did not survive the Bush administration.

The Bush administration came into office challenging the value of the agreement and froze contacts with the North. After receiving intelligence showing moves to build enrichment facilities, it confronted North Korean officials at an acrimonious meeting in Pyongyang in October 2002.

The United States halted fuel shipments a month later, and, in early 2003, the North Koreans expelled IAEA inspectors and withdrew from the Non-Proliferation Treaty. They proceeded to reprocess the fuel rods they had stored for a decade, producing enough plutonium, intelligence estimates say, for four to six nuclear warheads. In February 2005, the North Koreans announced they had manufactured nuclear weapons. Last week, they apparently made good on that declaration.

Blame aside, North Korea's emergence as the world's ninth nuclear power may be the most serious failure in non-proliferation history. Unlike India and Pakistan, which remained outside the system of international treaties, North Korea acted in defiance of those controls. Who might be next?

Diplomatic failure

Unlike Iraq, the attempt to stop North Korea's nuclear program has relied on the tools of diplomacy, accompanied by economic incentives and coercive sanctions.

But serious questions have been raised from the start about the sincerity and methods of the diplomatic efforts, particularly on the part of the United States and North Korea. The Bush administration has insisted -- and the president continues to make this argument -- that direct talks with North Korea do not work. Pyongyang has tried to frame everything as an issue with Washington, undermining talks that involved others, including South Korea.

Bush's stance lends credibility to those who charge the administration seeks "regime change," not a compromise that it believes will lend legitimacy to Kim Jong Il. The North Koreans now appear to have used the talks to buy time and build bombs.

Diplomacy has, at American insistence, consisted of six-party talks, held under Chinese auspices and including both Koreas, Japan and Russia. In truth, little real negotiating went on at these gatherings, at least until the last full round of talks in September 2005. In contrast to the thousands of hours of negotiations between Americans and North Koreans that led to the 1994 deal, there have been only tens of hours of actual give and take.

It is intriguing that the September agreement on a statement of principles for denuclearization came only after the State Department's chief negotiator was finally allowed to talk to his North Korean counterpart at length. Even then, their agreement evaporated almost immediately as they dueled publicly over the deal's meaning. American financial sanctions against North Korean currency counterfeiting further clouded the atmosphere, and direct contacts ground to a halt.

China's failure

The North Korean nuclear crisis is also a failure of China's bid for regional, if not global leadership. North Korea is an ally of China, a relationship that goes back more than half a century to the Korean War, when Chinese "volunteers" poured across the border to prevent an American victory. Their relationship has become more difficult since China embarked on market reforms while North Korea clung to its peculiar brand of Stalinism.

China has been torn between its loyalty to Pyongyang, its desire to maintain a stable balance of power in the region and its fear that the North's nuclear ambitions could provoke conflict on its borders. By becoming host for the six-party talks, Beijing stepped into an unusual leadership role.

The Bush administration was eager to move the burden of the North Korean problem onto the Chinese. Some administration hard-liners argued that China had the power to trigger the collapse of Kim Jung Il's regime by cutting off energy and food supplies.

Time and again, Beijing dragged the North Koreans back to the negotiating table, while also pushing Washington to engage Pyongyang in the talks. But Chinese irritation over American inflexibility has now been trumped by North Korea's defiance. Chinese policy-makers now wonder how they can punish the North without creating chaos, or war.

Failure of engagement

The final failure lies on the doorstep of South Korea's 10-year-long policy of engagement. The "sunshine policy" asserted that the North could be induced to give up its nuclear option by opening up the isolated communist state and promoting the forces of Chinese-style reform.

After a historic summit meeting in 2000, South Korean aid and trade, even tourists, flowed into the North. South Koreans lost their fear of a former foe, seeing it more as an impoverished lost brother than a mortal threat. Tensions with their American allies rose because of a gap in the North's perceived threat. The United States wondered why its troops should continue to defend South Korea.

Now South Koreans must confront the possibility that the North may have used engagement only to buy time.

THE TWO DANGERS

Threat of war

With eyes on Iraq and the Middle East, the Korean Peninsula has been far from the center of American attention. American forces based in South Korea and Japan have been dispatched to Iraq.

Yet the demilitarized zone that separates the two Koreas remains the most militarized frontier on the planet, with hundreds of thousands of well-armed soldiers poised against each other. Clashes along that frontier used to be commonplace and there are signs of a renewal of tensions. The danger of unintended escalation cannot be dismissed.

What might happen if a U.S. naval vessel, moving to inspect a North Korean freighter - as the U.N. resolution may authorize - is fired on or even captured, as the USS Pueblo was in 1968? It is a frightening scenario already worrying some at the Pentagon and the State Department.

Risk of proliferation

More than anything else, American policy-makers fear that North Korea, emboldened by its nuclear success and perhaps desperate for funds amid economic sanctions, might sell its nuclear expertise to Iran and others, including terrorist groups.

For Pyongyang, an alliance with Iran is a logical response to American and global pressure. The North Koreans have sold ballistic missiles to Tehran since the 1980s and rumors of nuclear cooperation persist.

An American effort to interdict the movement of ships and planes to Iran -- with possible U.N. backing - is probable. But the most likely transit is across the long and loosely controlled land border with China. The amount of plutonium needed to make a warhead is the size of a grapefruit and hard to detect - creating yet another nightmare scenario.

THE OPPORTUNITY

In this otherwise bleak landscape, there is an opportunity. For the first time, there is a chance of a consensus among the key players -- China, Japan, South Korea, Russia and the United States. The passage of a U.N. resolution is a small step in that direction. But the real test will come next, as the nations must cooperate to put pressure on North Korea, while coolly navigating the perils of war and making sure to leave open a diplomatic exit.

There is a slim chance of such concerted action, and a limited window for achieving it. Not everyone sees the dangers the same way. Signs of rethinking errors of the past are no more evident in Beijing and Seoul than they are in Washington or Tokyo. Ultimately, however, if they are to seize this moment of opportunity, all parties must face up to the fact that the policies of the past have failed.