Two Koreas Agree on Nuclear Ban North and South Korea announce that they have initialed an agreement banning nuclear weapons from the Korean Peninsula, but the two sides do not settle on measures to ensure compliance. North Korea Signs Accord on Inspections

After years of promises and false starts, North Korea signs an agreement to permit inspections of its seven sites at Yongbyon, the heavily guarded nuclear complex 60 miles north of Pyongyang.

American intelligence agencies had begun monitoring activity at Yongbyon in the 1980s, and evidence had been growing at that time that the North was preparing to convert waste from the reactor into weapons-grade plutonium.

Clinton Is Sworn In Bill Clinton is sworn in as the 42nd president of the United States. Confrontation Over Treaty

In a defiant move against international pressure to inspect its suspected nuclear weapons development program, North Korea announces it is withdrawing from the Nuclear Nonproliferation Treaty, which it ratified in 1985, but then rethinks the wisdom of withdrawal. The North begins stockpiling plutonium.

Non-nuclear states that sign the treaty pledge never to develop nuclear weapons and agree to international inspections.

North Korea Tests Missile

North Korea conducts what appears to be the first successful test of the country's homegrown midrange missile, raising Japanese fears that missiles could reach some of Japan's most populous cities.

The tests, conducted on the Sea of Japan, are believed to have involved the Nodong 1, a missile North Korea has been developing for several years and is preparing to export to Iran in return for oil. American intelligence officials have said that the missile is believed to be capable of carrying a payload of chemical weapons, or perhaps a small nuclear device, though designing one would be challenging for the North.

C.I.A. Says North Korea May Have Bomb

The Central Intelligence Agency tells President Bill Clinton that North Korea may have one or two nuclear bombs. But that is an estimate, and the intelligence is murky.

When the International Atomic Energy Agency, an arm of the United Nations responsible for monitoring nuclear installations worldwide, analyzed samples of North Korea's plutonium in 1992, it concluded that scientists had engaged in more extensive reprocessing than they had acknowledged.

The question became: How much more?

North Korea Grants Access to Plants

In February, North Korea averts a possible trade embargo by allowing one full inspection of seven atomic sites by the I.A.E.A.

But when inspectors arrive in March, the North refuses to let them take radioactive samples from critical parts of its nuclear reprocessing center at Yongbyon. The samples would probably have provided evidence of whether the North is still attempting to produce weapons-grade fuel from its limited supply of plutonium.

Inspectors Return to North Korea

I.A.E.A. inspectors return to North Korea to finish their inspection, concluding that the country is within days of obliterating evidence of how much, if any, nuclear fuel has been diverted to its weapons program.

The Pentagon says the spent fuel could provide enough material for four or five nuclear bombs.

The United States says that if the evidence is destroyed, it will have no choice but to seek economic sanctions, a measure Pyongyang has said it will consider an act of war.

North Korea Tests Cruise Missile North Korea tests a cruise missile designed to sink ships. American officials say the cruise missile is designed to hit ships at a range of more than 100 miles and is part of North Korea's broad effort to upgrade its conventional forces. North Korea Quits Atomic Agency

North Korea announces its withdrawal from the I.A.E.A. and says the agency's inspectors will no longer be allowed in the country. It also threatens to turn its stockpile of nuclear fuel into bombs; the C.I.A. warns that North Korea may already possess one or two bombs.

The Clinton administration reinforces the American military presence in South Korea, and for a while many in the White House fear a war could break out.

Former President Jimmy Carter, acting on his own, travels to the North, meeting President Kim Il-sung, the country’s founder, and striking a deal that averts confrontation. Emerging from North Korea, Mr. Carter says he believed Mr. Kim and thinks the leader is healthy enough to run the country for another 10 years.

President Kim Il-sung Dies Kim Il-sung dies suddenly. His son, Kim Jong-il becomes leader, inheriting an impoverished country with an uncertain place in a post-cold-war era. U.S. and North Korea Sign Pact

Negotiations following the Carter visit results in a deal:

North Korea agrees to freeze and then dismantle the complex in Yongbyon and open up two secret military sites to inspection by international experts.

In exchange, an international consortium will replace North Korea's current graphite nuclear reactors with new light-water reactors, which are considered less dangerous because they produce little weapons-grade plutonium. The U.S. and its allies also agree to provide fuel oil to the North.

First Missile Over Japan The North fires a two-stage Taepodong-1 missile over Japan and into the Pacific Ocean. The firing suggests that North Korea has greatly increased the range of its missiles. Bush Takes Office

George W. Bush is sworn in as the 43rd president of the United States.

In his first State of the Union Address, President Bush charges that Iran, Iraq and North Korea "constitute an axis of evil."

Admission of Nuclear Program Confronted by Bush administration officials with evidence that it had cheated on the 1994 agreement, North Korea admits that it has been conducting a major clandestine nuclear program using enriched uranium. It declares it has now ''nullified'' its agreement with the United States to freeze all nuclear weapons development activity. Reactor Restarted in North Korea, U.S. Concludes As the U.S. prepares to invade Iraq, the North decides to begin harvesting plutonium from its five-megawatt reactor at the Yongbyon nuclear complex. Mr. Bush makes little reference to the developments as the administration works to build support for an Iraq invasion. American satellites detect plutonium being carted away, presumably for conversion to bomb fuel. Six-Nation Talks Begin The United States, China, Russia, South Korea and Japan hold the first of several rounds of negotiations with North Korea in Beijing. North Korea Claims to Extract Fuel for Bombs

In a statement, North Korea says it has removed 8,000 spent fuel rods from a reactor at its main nuclear complex at Yongbyon as one of several ''necessary measures'' to bolster its nuclear arsenal.

But intelligence officials say they cannot verify the assertion and others express skepticism that North Korea’s action, even if confirmed, would significantly increase its weapons stockpile.

North Korea Says It Will Abandon Nuclear Efforts

North Korea agrees to end its nuclear weapons program in return for security, economic and energy benefits.

The United States, North Korea and four other nations participating in negotiations in Beijing sign a draft accord in which the North promises to abandon efforts to produce nuclear weapons and to re-admit international inspectors to its nuclear facilities.

The agreement appears to rescue a diplomatic process that appeared to be on the verge of collapse after multiple rounds of negotiations failed to produce even a joint statement of principles.

Missiles Fired by North The North launches seven missiles over the Sea of Japan, including a new Taepodong-2 model that is designed for long range but explodes soon after launch. Other nations condemn the tests, and the United Nations Security Council later passes a resolution condemning them. First Nuclear Test

North Korea says it has set off its first nuclear test, becoming the eighth country in history, and arguably the most unstable and most dangerous, to proclaim that it has joined the club of nuclear weapons states.

The test was something of a fizzle, a subkiloton explosion, but it was enough to win unanimous passage of a resolution that imposed new economic sanctions.

Six-Nation Talks Resume North Korea agrees to resume the six-nation nuclear disarmament talks. New Accord The United States and four other nations reach a tentative agreement to provide North Korea with roughly $400 million in fuel oil and aid, in return for the North's starting to disable its nuclear facilities and allowing nuclear inspectors back into the country. North Korea Demolishes Cooling Tower North Korea demolishes the cooling tower at its Yongbyon nuclear reactor site. The event was broadcast by international media at Pyongyang's invitation. New Setback Complaining that the Bush administration has not yet fulfilled a promise to remove North Korea from a list of state sponsors of terrorism, Pyongyang moves to resume the reprocessing of plutonium. U.S. Takes North Korea Off Terror List The Bush administration removes it from its list of states sponsoring terrorism after North Korea agrees to resume disabling its nuclear plant and to allow inspectors access to the declared nuclear sites. The decision outrages Vice President Dick Cheney, who opposed it. Six-Party Talks Collapse With the Bush administration leaving office, top representatives of six-nation talks on denuclearizing the Korean Peninsula meet but fail to reach an agreement on inspecting North Korea’s nuclear sites. The North subsequently says there will be no more talks and vows to increase its nuclear efforts, including uranium enrichment. Obama Takes Office Barack Obama is sworn in as the 44th president of the United States. Rocket Launching Over the Pacific North Korea defies the United States, China and a series of United Nations resolutions by launching a rocket that the country says is designed to propel a satellite into space, but that the United States views as an effort to prove it is edging toward the capability to shoot a nuclear warhead on a longer-range missile. Second Nuclear Test North Korea’s official news agency announces that the country has successfully conducted its second nuclear test, “on a new higher level in terms of its explosive power and technology of its control.” President Obama’s team, only four months in office, determines that it cannot do business with the North Korean government and essentially freezes the relationship. “The test made everyone a Korea hawk,’’ one of Obama’s advisers says. More Missiles Tested North Korea fires three missiles into the sea near Japan and says it is “fully ready for battle” against the United States. New U.N. Sanctions The Security Council votes unanimously on an enhanced package of sanctions that, among other things, calls upon United Nations members to inspect cargo vessels and airplanes suspected of carrying military material in or out of the country. South Korean Navy Ship Sinks in Disputed Waters

A South Korean warship, the Cheonan, blows up and sinks near the disputed western maritime border with North Korea, killing 46 sailors.

South Korea and its allies, including the United States, believe that a North Korean torpedo caused the disaster. The North denies being behind the sinking.

North Korea Shells South Korean Island

The South Korean military is in “crisis status” and threatens military strikes after the North fires dozens of shells at a South Korean island, killing two of the South’s soldiers and setting off an exchange of fire in one of the most serious clashes between the sides in decades.

The North blames the South for starting the exchange; the South acknowledges firing test shots in the area but denies that any have fallen in the North’s territory.

More Advanced Program Than Iran’s The Obama administration concludes that North Korea’s new plant to enrich nuclear fuel, revealed to an American scholar visiting its Yongbyon nuclear complex, uses technology that is significantly more advanced than what Iran had struggled over two decades to assemble, according to senior administration and intelligence officials. Kim Jong-il Dies North Korea's state-run news agency, K.C.N.A., reports that Kim Jong-il has died of a heart attack. Mr. Kim fostered a personality cult and had been grooming his third and relatively unknown son, Kim Jong-un, to be his successor. A New Leader

North Korea declares Kim Jong-un is “supreme leader” after two weeks of national mourning for his father, Kim Jong-il.

Mr. Kim is now commander of the 1.2 million-strong Korean People’s Army and general secretary of the Workers’ Party.

Freeze of Nuclear Efforts

In the first major policy move under Kim Jong-un, North Korea agrees to suspend nuclear weapons tests and uranium enrichment and to allow international inspectors to verify and monitor activities at its main reactor, as part of a deal that included an American pledge to ship food aid to the nation.

The agreement comes after two days of talks with American officials in Beijing.

Rocket Fails Moments After Liftoff

North Korea launched a rocket that the United States and its allies called a provocative pretext for developing an intercontinental ballistic missile that might one day carry a nuclear warhead.

But the much-publicized launching fails when the rocket carrying the satellite explodes in midair about one minute after liftoff. The rocket and satellite — which cost the impoverished country an estimated $450 million to build, according to South Korean government estimates — splintered into many pieces and plunged into the Yellow Sea.

The failed launching drew swift international condemnation, including the suspension by the United States of food aid.

Construction of Yongbyon An American-based institute, citing satellite imagery, says that North Korea has resumed construction of a nuclear reactor that would give the country a new source of spent nuclear fuel from which plutonium, a fuel for nuclear weapons, can be extracted. Successful Rocket Launching

North Korea successfully launches a long-range rocket into orbit, provoking the Obama administration and, to some degree, the Chinese.

With the surprise launching of a rocket that flew beyond the Philippines and apparently put an object into orbit, North Korea shows that after a series of failures it is clearing technical hurdles to mastering the technology needed to build an intercontinental ballistic missile, analysts say.

A Third Nuclear Test

North Korea confirms that it has conducted its long-threatened third nuclear test, according to the official news agency K.C.N.A., posing a new challenge for the Obama administration in its effort to keep the country from becoming a full-fledged nuclear power.

American officials will look for signs of whether the North, for the first time, has conducted a test of a uranium weapon, based on a uranium enrichment capability it has been pursuing for a decade. Even the best news about the test — that it was small by world standards — could have a dangerous downside if the North’s statement that it is learning to miniaturize bombs is true. That technology, which is extremely difficult to master, is crucial to being able to load a weapon atop a long-range missile that might one day reach as far as the United States mainland.

First Woman Sworn In as President of South Korea The country’s new president, Park Geun-hye, 61, was sworn into office, facing far more complicated fissures both within South Korea and with North Korea than her father did during his Cold War dictatorship, which ended with his assassination 33 years ago. Rodman and Kim Meet, Courtside

In one of the strangest sights in the history of accidental American diplomacy, Dennis Rodman, the tattooed, lip-studded former N.B.A. star, meets with the North Korean leader, Kim Jong-un, and proclaims him a “friend for life” while watching a basketball game during which the two conversed in English.

Mr. Rodman and the crew of Vice Media, which is producing an HBO series, are now the only Americans known to have met Mr. Kim. The meeting fit with a longtime pattern of frequently unconventional and always well-choreographed encounters with the Kim family, usually accompanied by a blitz of cold war-style propaganda.

U.N. Council Orders More Sanctions

The United Nations Security Council orders new economic sanctions against North Korea for its third nuclear test last month, unanimously approving a resolution that the United States negotiated with China, the North’s greatest protector.

The vote places potentially painful new constraints on North Korean banking, trade and travel; pressures countries to search suspect North Korean cargo; and includes new enforcement language absent from previous measures. But the provisions are in some ways less important than China’s participation in writing them, suggesting that the country has lost patience with the neighbor it supported in the Korean War.

1953 War Truce Nullified

North Korea declares that it will no longer abide by the 1953 armistice that halted the Korean War amid joint military drills conducted by the United States and South Korea.

Meanwhile, President Obama’s national security adviser, Thomas E. Donilon, announces that the Treasury Department will impose sanctions on a North Korean bank that specializes in foreign-exchange transactions.

The move also comes a few days after the North threatened to strike the United States with “lighter and smaller nukes.”

U.S. to Bolster Missile Defense to Deter Attack by North Korea

The United States says it will deploy additional ballistic-missile interceptors along the Pacific Coast by 2017, in response to North Korea’s tests of nuclear technology and long-range missiles. The new deployment will increase the number of ground-based interceptors to 44 from the 30 already based in California and Alaska.

North Korea Shuts Last Military Hot Lines to South

North Korea cuts off the last remaining military hot lines with South Korea, accusing President Park Geun-hye of pursuing her predecessor’s hard-line policy that the North blames for a prolonged chill in inter-Korean relations.

North Korea has already shut down Red Cross hot lines with South Korea and a communication line with the American military command in South Korea. But the North's decision to cut off military hot lines with South Korea is taken more seriously in Seoul because the Koreas have used those four telephone lines to control daily cross-border traffic of workers and cargo traveling to the North Korean border town of Kaesong.

U.S. Runs Practice Sortie in South Korea The American military carries out a rare long-range mission over the Korean Peninsula, sending two nuclear-capable B-2 stealth bombers on a practice sortie over South Korea, underscoring Washington’s commitment to defend its ally amid rising tensions with North Korea. North Korea Orders Missile Readiness, State Media Say

In response to the United States mission, North Korean state media say that Kim Jong-un ordered his missile units to be ready to strike the United States and South Korea, which South Korean officials said could signal either preparations for missile tests or just more blustering.

But the North Korean announcement is seen as part of a dangerously accelerating situation by both China and Russia.

Although North Korea has issued strident threats during previous joint American-South Korean military drills, Mr. Kim has been far more aggressive in issuing such threats personally than his father, Kim Jong-il, was. Unlike his father, who had expanded his power base from his youth, Mr. Kim was catapulted into top leadership after his father's death in 2011 and must build his credentials as head of his “military first” government, South Korean analysts and officials say.

North Korea Threatens to Restart Nuclear Reactor

North Korea's General Department of Atomic Energy announces that it will put all its nuclear facilities — including its operational uranium-enrichment program at Yongbyon and its reactors mothballed or under construction — to use in expanding its nuclear weapons arsenal.

It is the first time the North has said it will use the Yongbyon plant to make nuclear weapons.

U.S. Speeds Missile Defense to Guam

The United States announces that it is speeding the deployment of an advanced missile defense system to Guam in the next few weeks, two years ahead of schedule, in what the Pentagon says is a “precautionary move” to protect American naval and air forces from the threat of a North Korean missile attack.

The system — called Thaad, for Terminal High Altitude Area Defense — was scheduled for deployment around 2015.

North Korea Advises Embassy Evacuations

The North Korean government advises Russia, Britain and other countries to consider evacuating their embassies in Pyongyang amid rising tension there. Analysts in Russia and South Korea suggest that the North’s advisory is not an indication that Pyongyang is considering military action but is instead part of an unrelenting drumbeat of threats.

The Seoul stock market falls, and General Motors says it is making contingency plans for workers at its South Korean plants.

North Korea Pulls Out of Factories It Runs With South

North Korea says it will withdraw all its 53,000 workers and “temporarily suspend the operations" at Kaesong, an industrial park jointly run with South Korea, casting doubt on the future of the last remaining symbol of inter-Korean reconciliation.

The North’s final decision will depend on the South Korean government’s attitude, the country’s official Korean Central News Agency quoted Kim Yang-gon, a secretary of the Central Committee of the North’s ruling Workers’ Party of Korea, as saying.

North Korea Warns It Is on Brink of Nuclear War With South

North Korea warns foreigners that they might want to leave South Korea because the Korean Peninsula is on the brink of nuclear war.

There are no signs of panic in South Korea, and the American Embassy in the capital, Seoul, notes that the State Department’s travel notice about South Korea is unchanged and does not recommend any special precautions for American citizens living in South Korea or planning to visit.

Adm. Samuel J. Locklear III, the American commander in the Pacific, worries that the North Korean leader, Kim Jong-un, might not have left himself an easy exit to reduce tensions.

South Korea Moves to Defuse Tensions With the North

South Korea appears to ease its stance on North Korea by calling for dialogue to help defuse tensions, as President Park Geun-hye moves to calm foreign investors whose confidence the North has tried to shake with increasingly belligerent maneuvers.

Until now, South Korea has categorically rejected any early dialogue with the North, believing that doing so amid a torrent of North Korean threats to attack the South would amount to capitulation and would only embolden the North’s brinkmanship.

North Korea May Have Nuclear Missile Capability, U.S. Agency Says

The Pentagon’s intelligence arm, the Defense Intelligence Agency, says with “moderate confidence" that North Korea has learned how to make a nuclear weapon small enough to be delivered by a ballistic missile.

A week later, James R. Clapper Jr., the director of national intelligence, says the one-paragraph assessment was mistakenly declassified by the Pentagon’s intelligence agency, an inadvertent disclosure that revealed competing views on the country within the United States’ spy agencies.

President Obama implicitly dismisses the conclusion in an interview with NBC News.

Kerry Says North Korea Talks Are Possible, but Hints at Conditions

Secretary of State John Kerry says that the United States is prepared to reach out to Kim Jong-un if he makes the first move to abandon his nuclear weapons program.

Earlier in the week of his visit, Mr. Kerry warned the North Korean leader not to proceed with a test launching of its Musudan missile and underscores that North Korea would be defeated if a conflict broke out.

The U.S. has postponed tests of an intercontinental ballistic missile and toned down its statements in recent weeks to try to create an atmosphere in which talks with North Korea might begin

North Korea Sets Conditions for Return to Talks

North Korea demands the lifting of United Nations sanctions and an end to joint American-South Korean military exercises as preconditions for starting dialogue to defuse tension on the Korean Peninsula.

By making demands that both the United States and South Korea has no intention of accepting, North Korea signals that it will not stand down anytime soon from a military standoff that has lasted for weeks.

South Korea to Pull Remaining Workers From the North

South Korea says it is pulling out all its 175 remaining factory managers from the Kaesong Industrial Complex, escalating a standoff over the only remaining symbol of economic cooperation between the two countries.

The decision comes hours after North Korea rejected South Korea’s proposal for talks on the future of the industrial park, and told the South that it was free to withdraw its people from there.

So far, neither North nor South Korea has said publicly that it wants to shut the complex permanently.

North Korea Launches Missiles

North Korea begins launching a total of six short-range projectiles for the next three days, in what are believed to be tests of short-range guided missiles or rockets from multiple launchers, officials say.

South Korea fears the North's artillery and multiple-rocket launchers, which are massed along the border with the South and capable of delivering a barrage on the South’s densely populated capital, Seoul.

China Tells North Korea to Return to Talks

The Chinese leader, Xi Jinping, strikes a stern tone with the North Korean envoy, Vice Marshal Choe, saying that his country should return to diplomatic talks designed to rid North Korea of its nuclear weapons, according to a state-run Chinese news agency.

The personal envoy of Kim Jong-un has been in Beijing for three days on a mission to repair the prickly relationship with China, the North's biggest benefactor. Experts say that the North bridles at China’s insistence on paying low prices for its iron ore, and that Chinese officials are annoyed by the North’s defiance of entreaties to refrain from missile and nuclear tests.

South and North Korea Pave Way for Direct Talks

The two countries restore a cross-border hot line, with the South proposing that logistical talks be held Sunday to arrange a cabinet-level meeting.

The development came after North Korea, in a sudden change of heart, proposed a day earlier that the two Koreas hold their first government-to-government dialogue in years. The surprise overture unleashed a rapid sequence of proposals and counterproposals that raised hopes of a thaw on the divided Korean Peninsula after months of bellicose rhetoric.

Plans for Talks Collapse

An agreement between North and South Korea to hold high-level government talks this week collapses in a last-minute dispute over who should lead their delegations, according to South Korean officials.

South Korea says that the talks were canceled but that it was still open to dialogue with the North. The meeting in Seoul would have been the first senior inter-Korean dialogue in six years. The agreement had been seen as a clear sign that the two Koreas were easing tensions and moving toward a thaw after years of recriminations.

South Korea Pledges Millions in Aid for North

South Korea announces $7.3 million worth of humanitarian aid for North Korea, a conciliatory gesture that coincides with a call by the South for “one last round” of talks on restarting a jointly operated industrial complex.

Study Suggests North Korea Is Doubling Area Devoted to Uranium Enrichment

North Korea appears to have doubled the size of the area used to enrich uranium at its Yongbyon reactor complex in recent months, the Institute for Science and International Security reports, raising new concerns that the country could increase production of weapons-grade fuel.

Koreas Agree to Reopen Factory Park in North

North and South Korea agree to reopen Kaesong, a joint industrial complex, in a sign that the two sides are inching toward a thaw after months of high tension earlier this year.

The next day, President Park Geun-hye of South Korea proposes talks to reunite families separated by the Korean War six decades ago.

North and South Korea Exchange Fire

North Korea and South Korea fire hundreds of artillery shells across their disputed western sea border, escalating military tensions a day after the North threatened to conduct more nuclear tests. The shells fall harmlessly into the waters, but the exchange is the most serious episode along the border since an artillery duel in 2010.

It comes less than a week after North Korea's first tests of midrange projectiles in nearly five years. U.S. Commander Sees Key Nuclear Step by North Korea

The top American military commander in South Korea, Gen. Curtis M. Scaparrotti, said that he believed North Korea had most likely completed its yearslong quest to shrink a nuclear weapon to a size that could fit atop a ballistic missile. His assessment, if correct, could change American calculations about the vulnerability of the United States and its allies, and the North’s ability to sell nuclear weapons to others.

North Korea Threatens to Conduct Nuclear Test

The research organization, the Johns Hopkins University’s U.S.-Korea Institute at SAIS, reports on its website 38 North that recent commercial satellite imagery of the Yongbyon nuclear facility showed evidence that the country might be preparing to reprocess spent nuclear fuel to extract weapons-grade plutonium. Spent fuel from that reactor remains the North’s only known source of plutonium, fuel for its small arsenal of nuclear bombs.

A day later, in response to a United Nations committee’s recommendation to prosecute North Korean leaders for rights violations, the country threatens to conduct its fourth nuclear test.