But there were dozens of small clashes over the years along the DMZ, sometimes resulting in the deaths of South Koreans and Americans. Both sides built up enormous forces: Mr. Kim's army was 1.1 million strong, though in recent years it has spent much of its time building apartments and dams rather than training.

In 1968, as the Vietnam War raged, North Korea and Mr. Kim surged into the headlines again. The North seized an American intelligence ship, the Pueblo, and its crew stayed in prison for 11 years. In 1972 there were the first gestures of peace to the South, called the Red Cross Talks, in which both sides talked of allowing families divided by the war to meet. But those talks broke off and were not resumed for 18 years.

When they did come back together the two Koreas reached an historic accord: A December, 1991 agreement on peace and denuclearization. It was not a peace treaty. But it did provide for communications between the two Koreas: Roads, radio broadcasts, exchange of mail, mutual inspection of each other's military sites. None of that has happened, and relations worsened as the nuclear crisis deepened.

Starting last year, suddenly North Korea was back on Washington's agenda. The C.I.A. predicted the country could be a year to 18 months from building a bomb. Its ambitions -- to build a weapon that could threaten Seoul and Tokyo, and to assemble an arsenal of missiles to go with it -- has been the focus of America's security problems in Asia for two years now, as officials have tried to determine if the weapons project was a bargaining chip for economic aid or an effort to remain independent.

Mr. Kim devoted a huge amount of the country's scarce resources to building a nuclear complex centered on a 25 megawatt reactor based on old technology used by the British in the 1950's. The design uses ordinary uranium as fuel and graphite to control the nuclear reaction: The North has its own, ample supplies of both, meaning it does not have to worry about being cut off by foreign powers.

Conveniently, such old designs create waste that is high in plutonium content. The plutonium can be extracted and converted into bomb fuel with the right reprocessing technology. And the cat-and-mouse game over the past few years has been all about the North's steady progress in building that technology, while denying it all the way. For years the North denied it was building a reprocessing plant, even though a football-field sized one sticks out on satellite photographs. The Great Leader and the Dear Leader don't need a satellite: They have a guest cottage was built amid the complex. In the Spring, inspectors who got back into the non-existent reprocessing plant reported that a second manufacturing line was under construction -- to allow greater throughput.

In Washington, successive administrations sleepwalked through the evidence of the buildup. There was always another nuclear renegade to worry about: Qaddafi, Saddam, the Pakistanis. And time and time again, Washington convinced itself that this crisis was abating. When Mr. Kim signed the Non-Proliferation Treaty, leading everyone to sigh in relief, even if he then violated the treaty by barring inspectors for seven years. In 1991, the North and South signed an accord denuclearizing the Korean Peninsula and banning reprocessing on either side. Again there were cheers, and again the North ignored the ban, and kept building.

Every time there was talk of finally taking action, the Asian allies fretted that Kim should not be provoked. But the warning lights became impossible to miss in March, 1993, when the North announced it would pull out of the Nonproliferation Treaty rather than face continued pressure.