Here's a look at what you need to know about North Korea's nuclear capabilities and history.
1985 North Korea joins the Nuclear Non-Proliferation Treaty (NPT).
1993 International Atomic Energy Agency (IAEA) charges that North Korea is violating the NPT and demands that inspectors be given access to two nuclear waste storage sites.
North Korea threatens to quit the Nuclear Nonproliferation Treaty amid suspicions that it is developing nuclear weapons. It ultimately does not quit the program but agrees to inspections in 1994.
1994 North Korea and U.S. sign an agreement. North Korea pledges to freeze and eventually dismantle its nuclear weapons program in exchange for international aid to build two power-producing nuclear reactors.
1998 August 31 - North Korea fires a multistage rocket that flies over Japan and lands in the Pacific Ocean, proving the North Koreans can strike any part of Japan's territory.
November 17 - The U.S. and North Korea hold the first round of high-level talks in Pyongyang over North Korea's suspected construction of an underground nuclear facility. The United States demands inspections.
1999 February 27-March 16 - During a fourth round of talks, North Korea allows U.S. access to the site in exchange for U.S. aid in increasing North Korean potato yields. U.S. inspectors find no evidence of any nuclear activity during a visit to site in May.
September 13 - North Korea agrees to freeze testing of long-range missiles while negotiations with the U.S. continue.
September 17 - President Bill Clinton agrees to ease economic sanctions against North Korea.
December - A U.S.-led international consortium signs a $4.6 billion contract to build two nuclear reactors in North Korea.
2000 July - North Korea threatens to restart its nuclear program if the U.S. does not compensate it for the loss of electricity caused by delays in building nuclear power plants.
2001 June - North Korea warns it will drop its moratorium against testing missiles if the U.S. does not pursue normalized relations with North Korea. It also says it will restart its nuclear program if there is not more progress on two U.S.-sponsored nuclear power plants being built in North Korea.
2002 January 29 - President George W. Bush labels North Korea, Iran and Iraq an "axis of evil" in his State of the Union address. "By seeking weapons of mass destruction, these regimes pose a grave and growing danger," he says.
October 4 - U.S. officials, in closed talks, confront North Korea with evidence that they are operating a nuclear weapons program in violation of the 1994 nuclear agreement. Specifically, the U.S. has proof that they are operating a uranium enrichment facility. North Korea admits that is has been operating the facility in violation of the agreement. The information is NOT made public.
October 16 - The Bush Administration first reveals that North Korea has admitted operating a secret nuclear weapons program in violation of the 1994 agreement. They have NOT, apparently, admitted having any nuclear weapons.
December 22 - North Korea says it has begun removing IAEA monitoring equipment from nuclear facilities.
December 31 - North Korea expels IAEA inspectors.
2003 January 10 - North Korea withdraws from the Nuclear Nonproliferation Treaty.
February 5 - North Korea's official news agency says the nation has reactivated its nuclear power facilities.
February 24 - North Korea test fires a land-to-ship missile into the sea between the Korean Peninsula and Japan.
February 26 - The United States says North Korea has reactivated its five-megawatt nuclear reactor at Yongbyon.
March 10 - North Korea test fires another surface-to-vessel anti-ship missile into the Sea of Japan.
April 23, 2003 - Declares it has nuclear weapons.
August 27 - The U.S., North Korea, South Korea, China, Japan and Russia take part in talks about the crisis in North Korea.