This information below was introduced by an American trip friend of mine in Connecticut in August 2015. Thank you very much, T! (Lily)
Arms Control（https://www.armscontrol.org/factsheets/dprkchron）
Chronology of U.S.-North Korean Nuclear and Missile Diplomacy
Contact: Kelsey Davenport, Director for Nonproliferation Policy
Updated: April 2017
For years, the United States and the international community have tried to negotiate an end to North Korea’s nuclear and missile development and its export of ballistic missile technology. Those efforts have been replete with periods of crisis, stalemate, and tentative progress towards denuclearization, and North Korea has long been a key challenge for the global nuclear nonproliferation regime.
The United States has pursued a variety of policy responses to the proliferation challenges posed by North Korea, including military cooperation with U.S. allies in the region, wide-ranging sanctions, and non-proliferation mechanisms such as export controls. The United States also engaged in two major diplomatic initiatives in which North Korea to abandon its nuclear weapons efforts in return for aid.
In 1994, faced with North Korea’s announced intent to withdraw from the nuclear Nonproliferation Treaty (NPT), which requires non-nuclear weapon states to forswear the development and acquisition of nuclear weapons, the United States and North Korea signed the Agreed Framework. Under this agreement, Pyongyang committed to freezing its illicit plutonium weapons program in exchange for aid.
Following the collapse of this agreement in 2002, North Korea claimed that it had withdrawn from the NPT in January 2003 and once again began operating its nuclear facilities.
The second major diplomatic effort were the Six-Party Talks initiated in August of 2003 which involved China, Japan, North Korea, Russia, South Korea, and the United States. In between periods of stalemate and crisis, those talks arrived at critical breakthroughs in 2005, when North Korea pledged to abandon “all nuclear weapons and existing nuclear programs” and return to the NPT, and in 2007, when the parties agreed on a series of steps to implement that 2005 agreement.
Those talks, however, broke down in 2009 following disagreements over verification and an internationally condemned North Korea rocket launch. Pyongyang has since stated that it would never return to the talks and is no longer bound by their agreements. The other five parties state that they remain committed to the talks, and have called for Pyongyang to recommit to its 2005 denuclearization pledge.
2017
February 12, 2017: North Korea tests a new ballistic missile, the Pukguksong-2. North Korean media calls the test a success. The missile flew about 500 kilometers at a lofted trajectory. Imagery suggests that the Pukguksong-2 is a solid-fueled, medium-range system based on a submarine launched ballistic missile that North Korea has been testing for several years. The test utilized 'cold-launch' technology, meaning that the missile was ejected from its canister using compressed gas. The transport erector launcher used for the missile test was also domestically manufactured in North Korea.
February 13, 2017: Kim Jong Nam, the older half-brother of Kim Jong Un, is killed in an airport in Malaysia. Tests reveal that he died from exposure to VX, a nerve agent. VX is banned under the Chemical Weapons Convention, but North Korea has not signed or ratified that treaty. North Korea denies responsibility for the assasination.
March 6, 2017: North Korea launches four ballistic missiles from a region near North Korea's border with China. The missiles fly about 1,000 kilometers and land in Japanese economic exclusion zone, about 300 kilometers off the coast Japan.
April 5, 2017: North Korea tests a ballistic missile. The missile explodes shortly after the launch.
April 15, 2017: North Korea celebrates the birth of its founder, Kim Il Sung, with a parade that displays several new ballistic missiles, including a new variant of the KN-08 and two cannister systems. It is unclear if the cannisters hold new ICBMS.
April 16, 2017: North Korea tests a ballistic missile. The missile explodes shorterly after the launch.
April 26, 2017: The Trump Administration briefs Congress on its North Korea policy and releases a statement that calls for increasing sanctions pressure on North Korea and working with allies and regional partners on diplomacy.
April 27, 2017: Secretary of State Rex Tillerson says in an interview with NPR that the United States is open to direct talks with North Korea on the "right agenda." He says that denuclearization is still the goal for any agreement.
April 28, 2017: Secretary of State Rex Tillerson chairs a special meeting of the UN Security Council. In opening remarks he says that North Korea must take "concrete steps to reduce the threat that its illiegal weapons programs pose" before talks can begin.
（End）
