North Korea's claimed nuclear test has left Northeast Asia pondering how to deal with its new security environment. But the test hardly came as a surprise.
Six years ago, then South Korean President Kim Dae-jung declared that Koreans no longer needed to live with the constant threat of war. His historic 2000 summit with the North Korean leader Kim Jong Il raised hopes for peace and even eventual reunification between the two countries, bitterly divided since 1945.
U.S. and North Korean relations also were on the upswing. U.S. Secretary of State Madeleine Albright visited Pyongyang late in 2000 and met with Kim Jong Il.
That meeting came six years after the U.S. and North Korea had nearly gone to war, over Pyongyang's efforts to build nuclear weapons, an effort that began in the 1950s. The two countries in 1994 signed the Agreed Framework, which promised North Korea energy aid and other benefits for freezing its weapons program.
On Monday, the Pyongyang government said it had exploded a nuclear device - breaking its promises to the U.S. and the rest of the world not to do so.
Many arms experts and officials in the United States say North Korea probably began working toward that test in the late 1990s.
In 2001, President Bush took office and his administration decided to re-evaluate relations with Pyongyang, doubting the ability to verify its compliance with the Agreed Framework.
Later, President Bush made clear he did not trust Pyongyang.
"North Korea is a regime arming with missiles and weapons of mass destruction, while starving its citizens," he said. "States like these and their terrorist allies constitute an axis of evil arming to threaten peace in the world."
Then, in October of 2002, a senior U.S. diplomat, James Kelly, revealed Pyongyang's secret effort to enrich uranium - a fuel for nuclear weapons.
"I told the North that they must immediately and visibly dismantle this covert nuclear weapons program," he said.
The North responded to the revelations by re-opening its shuttered facility to reprocess nuclear fuel rods, expelling United Nations nuclear inspectors and abandoning the Nuclear Non-Proliferation Treaty.
In reaction, the U.S. and other nations cut off energy aid and other help to North Korea.
Washington's tougher stance against Pyongyang differed sharply from its ally South Korea's policy of engagement. By sending aid and investment to the North, the South hoped to coax Pyongyang into good behavior.
Some political analysts say Seoul got little for its efforts.
"South Korea should have been more strong against the possibility that North Korea [could] develop a nuclear program," said Chun Hong-chan, a politics professor at Pusan National University in South Korea. "It has been excessively accommodating."
To ease tensions, the United States, China, South Korea, Japan and Russia opened nuclear disarmament talks with the North in 2003.
As it has in other crises, Pyongyang swung from conciliation to provocation throughout the negotiations. It said it had manufactured nuclear weapons, then a year ago, it agreed in principle to abandon the nuclear programs in exchange for economic and security incentives.
But Pyongyang has refused to engage in further talks - apparently in anger over U.S. sanctions against alleged money laundering and counterfeiting.
Just a week before Pyongyang said it would conduct a nuclear test, North Korea's Deputy Foreign Minister Choe Su Hon told the U.N. General Assembly that the United States was imposing unjustified financial sanctions. He said under those conditions his government would not be able to return to negotiations.
"This is a matter of principle which we cannot tolerate even the slightest concession," said Choe.
In past crises, North Korea has often blustered and threatened, hoping to push the rest of the world to grant its demands.
But on Monday, the top U.S. envoy to the nuclear talks, Christopher Hill, said Washington would not play the North's brinkmanship game.
"I think what the North Koreans have in mind is that if they go ahead and test, we may be angry now but at some point we'll get over it and will deal with them as nuclear-weapons state," said Hill. "We're not going to deal with them as a nuclear-weapons state. They've got to get out of this business."
Some arms control experts say it is possible that Pyongyang never intended to stop its nuclear programs - that the isolated country feels it must have the weapons to protect itself or to bully other nations.
They say that the threat of increased United Nations sanctions is not likely to push the country's leaders to give up nuclear weapons. After all, if Monday's test is confirmed, North Korea has just fulfilled a 50-year quest to become a nuclear power.