Some key developments in Kim's diplomacy:
Jan. 1, 2018: Kim in his annual New Year's address calls for improved relations with South Korea and offers to send a delegation to the Winter Olympics.
February 2018: Hundreds of North Koreans attend the Pyeongchang Games, including Kim's sister, who conveys her brother's desire for a summit with South Korean President Moon Jae-in.
March 7, 2018: A South Korean envoy returns from visiting Pyongyang and says Kim is willing to discuss his nuclear arsenal with Washington. Days later, President Donald Trump accepts Kim's invitation to meet.
March 27, 2018: Kim makes a surprise visit to Beijing to meet with Xi.
April 21, 2018: North Korea says it has suspended nuclear and long-range missile tests and is shifting its focus to improving its economy. Trump tweets the move is "big progress!"
April 27, 2018: Kim meets Moon at the inter-Korean border and they make aspirational comments in favor of a nuclear-free peninsula and permanent peace.
May 7, 2018: Kim meets Xi again in China and calls for stronger strategic cooperation between them.
May 9, 2018: U.S. Secretary of State Mike Pompeo visits Pyongyang to prepare for the planned Trump-Kim meeting. North Korea frees three Americans who had been imprisoned.
May 24, 2018: North Korean diplomat Choe Son Hui releases a statement berating Vice President Mike Pence for his critical comments on the North and saying it was up to the Americans whether they would "meet us at a meeting room or encounter us at nuclear-to-nuclear showdown." Trump announces he's pulling out of his summit with Kim, citing the North's "tremendous anger and open hostility."
May 26, 2018: Kim and Moon meet at the inter-Korean border in an effort to revive the summit with Trump. Moon says Kim reaffirmed his commitment to denuclearize but also said he was unsure whether he could trust Washington to provide security guarantees in return.
June 1, 2018: After meeting North Korean envoy Kim Yong Chol at the White House, Trump says his meeting with Kim Jong Un is back on.
June 12, 2018: Trump and Kim meet in Singapore, where they repeat the first inter-Korean summit's vague statement on the peninsula's denuclearization without describing when and how it will occur.
June 19, 2018: Kim visits Beijing for his third meeting with Xi, who praises the "positive outcome" of the Trump-Kim meeting.
Sept. 19, 2018: Kim and Moon hold their third summit in Pyongyang. The North says it's willing to permanently dismantle its main nuclear complex in Yongbyon if the United States takes corresponding measures.
Jan. 1, 2019: Kim in his New Year's speech says he hopes to continue his nuclear summitry with Trump, but also that he would seek a "new way" if the United States persists with sanctions and pressure against the North.
Jan. 8, 2019: Kim visits Beijing for his fourth summit with Xi, vows to "achieve results" on the nuclear standoff in his second meeting with Trump.
Feb. 8, 2019: Trump announces Hanoi, Vietnam, as the venue of his second summit with Kim.
Feb. 27-28, 2019: Trump and Kim's second summit breaks down over what the Americans describe as excessive North Korean demands for sanctions relief in exchange for partial disarmament steps limited to the Yongbyon complex.
April 13, 2019: Kim says he is open to another meeting with Trump, but sets the year's end as a deadline for Washington to offer mutually acceptable terms for an agreement to salvage the diplomacy.
April 25, 2019: Kim meets Russian President Vladimir Putin in Vladivostok. Putin says Kim would require strong security guarantees in order to abandon his nuclear program.
May 9, 2019: North Korea fires two short-range missiles toward the sea in its second launch in five days, ending a pause in ballistic testing. The launches are seen as measured efforts to dial up pressure on Washington and Seoul without actually causing the negotiations to collapse.
June 17, 2019: North Korea and China announce Xi will visit North Korea on Thursday and Friday.