The stunning announcement that US President Donald Trump and North Korean leader Kim Jong Un will hold an unprecedented meeting is the latest and most astonishing step forward in a flurry of diplomacy.
The two and their respective allies fought each other to a ceasefire in the 1950-53 Korean War and Pyongyang has for decades defied heavy sanctions to pursue its nuclear weapons and ballistic missile programmes, developing rockets that can reach the US mainland.
But it has offered to put them on the negotiating table if what it calls threats against it are eliminated. Here are some questions and answers on the dramatic developments.
Where will the summit be?
All that has been confirmed so far is that the meeting will take place by the end of May.
If it happens in Pyongyang, Kim is sure to put on a spectacular show for his visitor, but for America it would run the risk of appearing that Trump is coming to pay his respects.
The Demilitarized Zone that divides the two Koreas - where Kim and South Korean President Moon Jae-in are to meet in late April - is probably the favourite at this stage, offering ease of access for both sides, a controlled environment, and facilities already in place.
It would also appeal to the two men's sense of drama.
A more neutral location with less weight of symbolism such as Beijing or Geneva - Kim was educated in Switzerland - would mean the three key players would have to plan events with another host nation.
Furthermore, it would involve a journey on both sides and Kim has not left the North since inheriting power from his father in 2011.
Seoul would most likely be unthinkable to Pyongyang, and Washington even more so, but on the other hand no one would have predicted three months ago that Kim's sister would visit the South Korean capital within weeks.
United Nations headquarters in New York - Trump's home town - would mean Kim stepping on American soil but it has a long history of hosting a rogues' gallery of world leaders.
Events have moved so far, so quickly and in such unforeseen ways that no option can immediately be ruled out.
How will Trump prepare?
The announcement on the White House lawn came almost exactly 24 hours after Secretary of State Rex Tillerson said the US was "a long way from negotiations" with the North.
The North's diplomats are renowned as tough, wily negotiators - "very Machiavellian" in the words of one analyst.
But under Trump the State Department has lost many Korea specialists and he has yet to name an ambassador to Seoul - front-runner expert Victor Cha was reportedly ruled out of consideration because of his refusal to entertain the idea of a pre-emptive US strike on the North.
The US Special Representative for North Korean policy Joseph Yun retired last week, and there has been none of the diplomatic groundwork that usually precede a meeting between heads of state.
"Summits normally come at the end of a long series of negotiations at lower levels in which lots of devils in the details are hammered out," said Pusan National University associate professor Robert Kelly.
"Trump, always the publicity-seeker, is just diving right in," he tweeted, warning there was a risk he "will wander from decades of joint US-South Korea policy, about which he naturally knows nothing, and make some kind of deal for a 'win' that no other US official would endorse".
How will the two get on?
The two men are radically different but in other ways strikingly similar. Kim was chosen to inherit power and was groomed to do so for years, while Trump is one of the unlikeliest US presidents in history, reaching the White House via a career in property development and reality television.
Kim has far more experience in office - more than six years - and expects to rule for decades, planning for the long term accordingly with no concern about the next day's headlines in his state-controlled media.
But both men prize personal loyalty, counting family members among their closest advisers, and they share a taste for theatre - Trump has called for a military parade in Washington, something Kim holds in Pyongyang usually every year.
They traded threats and personal insults last year, with Trump dubbing Kim "little Rocket Man" while menacing the North with "fire and fury" that would "completely destroy" the country.
In turn Kim called him a "mentally deranged US dotard".
But Trump is known for his sudden turnarounds and tweeted in November: "I try so hard to be his friend - and maybe someday that will happen!"
What is South Korea's role?
Strikingly, all the key announcements of recent days have been made by South Korea.
Its envoys revealed both North Korea's willingness to negotiate over its nuclear weapons and - on the White House lawn, with no US officials present - Trump's acceptance of the offer to meet.
In the early months of Donald Trump's presidency he focussed on China as a way to influence the North and developed a friendship with Japan's Shinzo Abe, leading to fears in Seoul that the South was being bypassed - reinforced when he accused President Moon Jae-in of "appeasement".
But Moon has seized the opportunity presented by the Winter Olympics to try to broker talks between the rivals - while repeatedly crediting Trump's assertive approach for Kim's willingness to talk.
How will China react?
For decades Beijing has been Pyongyang's key diplomatic protector and main source of trade and aid, but their relationship has soured in recent years.
Kim has not travelled to Beijing to pay his respects to President Xi Jinping, and Beijing has become increasingly frustrated with its neighbour's behaviour, showing a new willingness to agree to tougher sanctions against it - and enforce them.
At the same time it fears the collapse of the regime in Pyongyang and the instability it would bring, potentially sending waves of refugees into China and the possibility of US troops stationed on its border in a unified Korea.
As such it will welcome an agreement - for years it has been urging the resumption of the Six-Party Talks process it chaired. And after Seoul announced an historic inter-Korean summit this week, Beijing said it was "cheering them on".
Any agreement that could lead to a reduced US troop presence in the South would also by implication tilt the balance of power in Beijing's favour in a region it increasingly sees as its own back yard.
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