Here is a timeline of key events relating to North Korea's nuclear weapons program and Pyongyang's relations with the United States.
July 27, 1953
Armistice signed by United States, China, and North Korea brings an end to Korean War hostilities and establishes a de facto border between North Korea and South Korea known as the Korean Demilitarized Zone (DMZ).
January 1968
North Korea captures the U.S. Navy intelligence ship, USS Pueblo -- starting an 11-month prisoner drama and major Cold War crisis known as the "Pueblo incident."
April 15, 1969
U.S. Navy reconnaissance plane, EC-121, shot down over Sea of Japan by North Korea, killing 31 Americans.
February 1974
North Korea’s founding leader, Kim Il Sung, designates Kim Jong Il, his oldest son, as his successor.
August 18, 1976
Two U.S. soldiers on a routine tree-clearing operation in the DMZ are killed with their axes by North Korean troops -- creating a major diplomatic crisis.
December 12, 1985
North Korea ratifies the international Nuclear Non-Proliferation Treaty, barring the country from producing nuclear weapons and requiring regular inspections by the International Atomic Energy Agency (IAEA).
1986
A 5-megawatt experimental nuclear reactor at North Korea’s Yongbyon Nuclear Scientific Research Center becomes operational.
1990
North Korea successfully produces a small amount of plutonium.
September 17, 1991
Both North Korea and South Korea admitted as members of the United Nations.
April 10, 1992
North Korea's NPT Safeguards Agreement with the IAEA comes into force.
February 25, 1993
The first North Korean nuclear crisis begins as the IAEA accuses Pyongyang of NPT violations and demands that IAEA inspectors be given access to nuclear waste sites.
March 12, 1993
North Korea announces its intention to withdraw from the NPT.
May 29, 1993
North Korea test-fires a medium-range Nodong-1 ballistic missile into the Sea of Japan. Its estimated range is up to 1,500 kilometers with a 1,000-kilogram payload.
June 11, 1993
U.S. convinces North Korea to suspend its withdrawal from the NPT just one day before the decision was to come into effect.
July 8, 1994
North Korean leader Kim Il Sung dies. Kim Jong Il succeeds him.
October 21, 1994
First nuclear crisis ends as North Korea and U.S. sign Agreed Framework. In exchange for aid -- heavy fuel oil and two proliferation-resistant light-water nuclear reactors -- Pyongyang promises to halt construction and operation of nuclear reactors suspected of being part of a covert weapons program.
1994-1998
Economic mismanagement, loss of Soviet support, and major flooding followed by drought lead to famine. Some 3 million North Koreans reportedly starve to death.
April 4, 1996
North Korea abandons the 1953 armistice and begins sending thousands of troops into the DMZ.
June 13-15, 2000
The first inter-Korean summit is held in Pyongyang between Kim Jong Il and South Korean President Kim Dae-jung. The summit paves the way for working talks, the reopening of border liaison offices, and family reunions. The South also grants amnesty to more than 3,500 North Korean prisoners.
January 29, 2002
U.S. President George W. Bush describes North Korea, Iraq, and Iran an "axis of evil" for continuing to build "weapons of mass destruction.”
October 16, 2002
The second North Korean nuclear crisis begins with Washington announcing that North Korea officials have admitted to a secret weapons-grade uranium-enrichment program in violation of 1994 Agreed Framework commitments.
November 11, 2002
The United States, Japan, and South Korea -- declaring they are no longer bound by the Agreed Framework -- decide to halt oil shipments to North Korea under the 1994 deal.
December 12, 2002
North Korea responds to oil supply cuts by announcing it will reactivate nuclear facilities at Yongbyon and expel IAEA nuclear inspectors.
December 22, 2002
North Korea starts removing UN monitoring devices from the Yongbyon nuclear plant.
January 10, 2003
North Korea announces its withdrawal from the NPT.
February 6, 2003
North Korea announces its nuclear facilities have been reactivated for "energy generation," claiming oil supply cuts left it no choice.
February 12, 2003
The IAEA confirms North Korea has violated nuclear safeguards and refers the issue to the UN Security Council.
May 12, 2003
North Korea pulls out of its last international nonproliferation accord -- a 1992 agreement with South Korea to keep the Korean Peninsula free of nuclear weapons.
August 1, 2003
North Korea agrees to six-party nuclear talks involving China, North and South Korea, the United States, Japan, and Russia.
August 27-29, 2003
Six-nation nuclear talks in Beijing fail to resolve differences between the United States and North Korea. Two additional rounds of talks will be held in Beijing during 2004.
October 2, 2003
North Korea declares it has completed the reprocessing of 8,000 spent nuclear fuel rods -- enough weapons-grade plutonium to develop as many as six nuclear bombs within months.
September 28, 2004
North Korea admits publicly for the first time that it has produced nuclear weapons, with Vice Foreign Minister Choe Sun Hon telling the UN General Assembly that the weapons were needed for "self-defense" against a "U.S. nuclear threat."
February 10, 2005
North Korea indefinitely suspends its participation in six-party talks over its nuclear program.
May 11, 2005
Shortly after test firing a short-range missile into the Sea of Japan, North Korea announces it is extracting more weapons-grade uranium from Yongbyon in order to "increase its nuclear arsenal."
July 25, 2005
Fourth round of six-nation nuclear talks begin in Beijing.
August 7, 2005
Recess called in six-nation nuclear talks as negotiators reach an impasse.
July 4, 2006
North Korea test fires at least six missiles. A long-range Taepodong-2 missile crashes shortly after take-off despite reportedly being able to target the United States.
October 9, 2006
North Korea announces it has conducted its first nuclear weapons test.
October 14, 2006
The UN Security Council imposes economic and commercial sanctions on North Korea over its nuclear weapons test.
December 18-25, 2006
Six-party talks resume for a fifth round. After a week, Pyongyang declares it will give up all of its nuclear activities and rejoin the NPT.
February 13, 2007
The fifth round of six-party talks concludes with Pyongyang promising to shut down the Yongbyon reactor in exchange for 50,000 metric tons of heavy fuel oil as part of an aid package.
July 14, 2007
North Korea shuts down it main Yongbyon reactor after shipments of heavy fuel oil begin. Shipments continue after the IAEA confirms the shutdown.
October 2-4, 2007
The second inter-Korean summit in Pyongyang leads to a peace declaration calling for international talks to replace the 1953 armistice. President Roh Moo-hyun becomes the first South Korean leader to walk across the DMZ.
March 27, 2008
North Korea expels all South Korean officials from an inter-Korean industrial complex to the north of the DMZ -- a marked deterioration of North-South relations. South Korea’s new president, Lee Myung-bak, takes a harder line against the North.
August 22, 2008
North Korean ruler Kim Jong Il suffers a stroke.
October 11, 2008
U.S. removes North Korea from its terrorist blacklist; Pyongyang agrees to provide full access to the Yongbyon nuclear site.
January 30, 2009
With North-South relations continuing to deteriorate, Pyongyang announces it is scrapping a non-aggression pact and all other military and political accords with the South.
April 2009
North Korea launches a long-range rocket, saying that it carried a communications satellite. South Korea and Japan accuse Pyongyang of testing long-range missiles. After criticism from the UN Security Council, North Korea walks out of six-party talks and restarts its nuclear facilities.
May 25, 2009
North Korea conducts its second underground nuclear test along with two short-range missile tests.
August 20, 2009
North Korea makes conciliatory gestures to South Korea, sending a delegation to the funeral of former President Kim Dae-jung, releasing four South Korean fishermen, and agreeing to resume family reunions.
March 26, 2010
North Korea sinks a South Korean warship, the ROKS Cheonan, near the sea border.
December 28, 2011
North Korean ruler Kim Jong Il dies. His second child, Kim Jong Un is declared supreme leader after overseeing the funeral and formally starts taking over key posts in April 2012.
April 4, 2012
A North Korean three-stage rocket launch, seen internationally as an illegal test of the long-range Taepodong-2 missile, fails.
October 9, 2012
After Washington and South Korea announce a deal to bolster South Korea’s ballistic missile program, North Korea claims it has missiles than can hit the U.S. mainland.
December 12, 2012
Following the failed April 2012 rocket launch, North Korea successfully sends a "rocket-mounted satellite" into orbit.
January 22, 2013
UN Security Council expands economics sanctions against North Korea in response to its December 12, 2012, rocket launch.
February 12, 2013
North Korea stages its third nuclear test, said to be more powerful than the 2009 test.
February 15, 2013
The European Union announces tighter economic sanctions on North Korea over its latest nuclear test.
March 7, 2013
The UN Security Council approves more sanctions over North Korea's latest nuclear test. North Korea amplifies threatening rhetoric by saying it could launch a pre-emptive nuclear strike against its enemies.
March 8, 2013
North Korea ends all peace pacts with South Korea, closing the main border crossing within the DMZ.
March 15, 2013
U.S. Defense Secretary Chuck Hagel announces expanded ballistic missile defense system deployments in Alaska in response to the North Korean nuclear threat.
April 2013
North Korea says it will restart all facilities at the Yongbyon nuclear complex. U.S. Secretary of State John Kerry warns Pyongyang that North Korea would lose any military confrontation with the United States. The Pentagon orders missile defense equipment and nuclear-capable stealth bombers to be moved to South Korea and Guam.
March 26, 2014
North Korea test-fires two medium-range Nodong ballistic missiles for the first time since 2009. The launches violate UN Security Council resolutions and come just hours after talks in the Netherlands between U.S., South Korean, and Japanese officials.
September 15, 2015
North Korea confirms that the Yongbyon nuclear facility is back in operation. Pyongyang threatens a nuclear attack against the United States as Washington calls on North Korea to fulfill its international obligations.
December 8. 2015
Washington imposes additional sanctions against North Korea over weapons proliferation. The expanded sanctions target the North Korean Army's Strategic Rocket Force, state banks, and shipping companies.
January 6, 2016
North Korea claims to have carried out its first hydrogen bomb test. Experts express skepticism.
February 7, 2016
North Korean claims it successfully put a satellite in orbit with a long-range rocket launch.
August 24, 2016
North Korea successfully launches a ballistic missile from a submarine.
September 5, 2016
North Korea test launches three ballistic missiles. At least one enters Japan’s air defense zone.
November 30, 2016
The UN Security Council imposes more sanctions that aim to cut North Korea's coal exports by 60 percent.
January 1, 2017
Kim Jong Un says North Korea is in the final stages of developing long-range guided missiles capable of carrying nuclear warheads that can strike the United States.
January 3, 2017
U.S. President-elect Donald Trump derides Kim Jong Un’s claims that North Korea will soon be able to target parts of the United States with a nuclear weapon, saying in a Twitter message "It won’t happen."
February 12, 2017
A new medium long-range ballistic missile, the Pukguksong-2, is fired by North Korea into the Sea of Japan.
March 6, 2017
Four ballistic missiles fired by North Korea into the Sea of Japan. Three fall into Japan’s exclusive economic zone within 320 kilometers of the Japanese coast.
April 2017
After several months of North Korean missile tests and increasingly hostile rhetoric, Washington warns North Korea that it must halt all of its nuclear and ballistic missile tests.
July 4, 2017
Pyongyang successfully test fires a long-range Intercontinental Ballistic Missile (ICBM) into the Sea of Japan. Experts estimate the missile could potentially reach Alaska.
July 28, 2017
North Korea carries out its second ICBM test launch, with Western experts saying it theoretically could have reached Los Angeles, Denver, or even Chicago. The United States and South Korea discuss possible "military response options."
July 29, 2017
Kim Jong Un claims the entire U.S. mainland is within reach of North Korea’s ICBMs; U.S. President Donald Trump vows to "take all necessary steps to ensure the security of the American homeland and protect our allies in the region." U.S. Secretary of State Rex Tillerson warns that Washington "will never accept a nuclear-armed North Korea."
July 30, 2017
U.S. President Donald Trump calls North Korea’s banned missile program a "grave and growing" threat.
August 8, 2017
U.S. President Donald Trump says North Korea "will be met with fire and fury like the world has never seen" if it threatens the United States again.
August 9, 2017
North Korea announces it is examining plans for an attack with "enveloping fire" against U.S. military facilities near the strategic U.S. Pacific island of Guam.