The Hanoi meeting ended after Kim demanded that all economic sanctions against North Korea be lifted in return for concessions on Pyongyang's nuclear program. "We couldn't do that," Trump later told reporters.
Trump showing strength by walking away from the negotiating table was preferable to him meeting Kim's demands, according to Tomohiko Taniguchi, one of Japanese President Shinzo Abe's senior policy advisers.
While Tokyo has long wanted a deal, ensuring it's the right deal is crucial, Taniguchi said.
"This 'friendly walk-away' was much better than giving a wrong signal to Kim Jong Un," he added. "Mr. Trump succeeded in setting in place the kind of dynamics between the two — one begging and the other refusing."
Japan is within easy striking distance of North Korean weapons and doesn't want to be left behind as negotiations proceed. It is also seen as a U.S. bulwark in the region and houses tens of thousands of U.S. troops and their high-tech equipment.
Abe has said Japan would not normalize diplomatic ties with Pyongyang or provide economic assistance until North Korea gave a full accounting of all abductees and return any of those taken who are still alive.
Kim and Trump held a one-on-one session in Hanoi, Vietnam, on Thursday morning that was followed by a meeting with a larger group of officials from both sides. But everything fell apart around the lunch hour.
South Korean President Moon Jae-in spoke to Trump for 25 minutes after the summit was called off.
"We do regret that President Trump and Chairman Kim Jong Un did not reach a complete agreement at today's summit,” said Kim Eui-keum, a spokesman for Moon. “But it is clear that (the summit) made more meaningful progress than any other time in the past."
He added: "President Moon noted President Trump's efforts made over an extended time to hold deep discussions in order to achieve the common goal of denuclearization and the establishment of the permanent peace on the Korean Peninsula. He also said that President Moon is looking forward to a good result in follow-up negotiations since the leaders confirmed each other's positions and discussed specific items in person."
Things began to change after the election in 2017 of Moon, a liberal human-rights lawyer, as South Korea's president who has met with Kim in an effort to lessen tension.
Trump called Kim “quite a guy and quite a character” and characterized his relationship with the dictator as “very strong” before departing Vietnam for Washington.
Despite the satisfaction expressed in Seoul and Tokyo, some critics charged that the U.S. team arrived at the Hanoi meeting unprepared for the complicated and intense negotiations, which resulted in the talks breaking down.
“This is a total failure, there is no other way to put it,” said Victor Cha who led the Asia division of former President George W. Bush's National Security Council. “It shouldn't have happened, the spade work should have been done in advance.”
Wendy Sherman, who helped to negotiate the Iran nuclear deal and was a close aide to then-Secretary of State Madeleine Albright when she visited Pyongyang in October 2000, said last year's meeting between the two leaders in Singapore — which produced a short statement that was light on details — was unorthodox but not necessarily a failure.
But the stakes were higher this time around, according to Sherman.
“The second time you actually have to accomplish something," she told MSNBC early Thursday. “It clearly wasn’t negotiated to the point that everyone was ready to sign. This was like a shotgun wedding out of the bromance.”
F. Brinley Bruton
F. Brinley Bruton is senior editor in charge of NBC News Digital’s London bureau.
Stella Kim, Linda Givetash and Reuters contributed.