Korea has been divided since 1945. The Korean War of 1950–1953 ended with an armistice agreement but not a peace settlement. A sporadic conflict has continued, with American troops remaining in the South as part of a mutual defense treaty. The North began building a nuclear reactor in 1963, and it began a nuclear weapons program in the 1980s. North Korea first committed to denuclearization in 1992 in the Joint Declaration of the Denuclearization of the Korean Peninsula. In a speech authored by David Frum, President George W. Bush referred to North Korea as part of an "axis of evil" during his 2002 State of the Union address, but in the 2005 Joint Statement of the Fourth Round of the Six-Party Talks, North Korea reaffirmed the 1992 Joint Declaration and the goal of verifiable denuclearization of the Korean Peninsula. In 2008, North Korea voluntarily gave information on its nuclear program in exchange for sanction relief, and they were taken off the list. Despite this, nuclear inspectors were barred from surveying any North Korean weapons facilities. The Obama administration had a policy of "strategic patience", in which provocations would not be rewarded with presidential attention or the sending of high-level envoys but instead be punished with sanctions and greater military coordination with South Korea and Japan. More nuclear tests were conducted in the succeeding years, and the 2010 bombardment of Yeonpyeong markedly raised tensions between North Korea and South Korea. The escalation of North Korea's nuclear program advanced particularly under the rule of Kim Jong-un, who became the leader in December 2011, after his father Kim Jong-il died.
Donald Trump was elected US President in 2016 with a position of opposition to Barack Obama's policy of "strategic patience" towards North Korea. While advocating a tough stance, he also expressed openness to dialogue, saying he would be prepared to "eat a hamburger" with Kim. He put himself at odds with military allies, saying that it would be better if South Korea and Japan protect themselves. In return, a North Korean-linked website described him as a "wise politician". In 2017, Moon Jae-in was elected President of South Korea with a promise to return to the Sunshine Policy of friendly relations with the North.
North Korea successfully tested its first intercontinental ballistic missile (ICBM), named Hwasong-14, in July 2017. In response to heightened North Korean rhetoric, Trump warned that any North Korean attack "will be met with fire, fury and frankly power, the likes of which the world has never seen before". In response, North Korea announced that it was considering a missile test in which the missiles would land near the US territory of Guam, but this was later postponed. North Korea tested what some sources argued may have been its first hydrogen bomb on September 3. The test was internationally condemned, and further economic sanctions were put on North Korea. The United States also added North Korea back to its State Sponsors of Terrorism list after nine years. On November 28, North Korea launched the Hwasong-15, which, according to analysts, would be capable of reaching anywhere in the United States. The United Nations responded by placing further sanctions on the country. After North Korea claimed that the missile was capable of "carrying [a] super-heavy [nuclear] warhead and hitting the whole mainland of the U.S.", Kim-Jong-Un announced that they had "finally realized the great historic cause of completing the state nuclear force", putting them in a position of strength to push the United States into talks.
Moon Jae-in (standing, lower left) with the North Korean representatives (upper right) and U.S. Vice President Mike Pence (lower right) at the PyeongChang Olympics
In his New Year address for 2018, North Korean leader Kim Jong-un celebrated completing their nuclear capabilities and proposed talks for sending a delegation to the upcoming Winter Olympics in South Korea. In January a false missile alert alarmed Hawaii. The Seoul–Pyongyang hotline was reopened after almost two years. North Korea sent an unprecedented high-level delegation, headed by Kim Yo-jong, sister of Kim Jong-un, and President of the Presidium of the Supreme People's Assembly Kim Yong-nam, and including performers like the Samjiyon Orchestra. The delegation passed on an invitation to President Moon to visit North Korea. The United States was represented by Vice President Mike Pence. After arriving late to a dinner hosted by President Moon, he was asked to greet the other dignitaries, but he shook hands with everyone except Kim Yong-nam and left early. North and South Korean athletes marched together in the Olympics opening ceremony and fielded a united women's ice hockey team.