It has been a frightening few weeks. United States President Donald Trump and North Korean leader Kim Jong Un have been trading threats and insults more recklessly than we have ever seen before from leaders in command of nuclear weapons.
No wonder the danger of nuclear war has seemed greater than at any time since the darkest days of the Cold War.
So where does the confrontation go from here? Is there any reason to hope that the tensions will ease? Or is the risk of conflict as high as ever? That all depends on a simple question: Will North Korea keep developing and testing its intercontinental ballistic missiles (ICBMs)?
Amid all the chest-thumping on both sides, it is important to remember that this is the real cause of the current crisis in North-east Asia. There is a reason for that. The prospect of a North Korean ICBM capability is a big deal. Pyongyang has had nuclear weapons for a decade, and - though no one likes to admit it - we have learnt to live with them.
But so far the North could launch a nuclear attack against only its closer neighbours, especially South Korea and Japan.
That changes if and when the North can field an operational ICBM. For the first time, Pyongyang's leaders could mount a direct nuclear attack on an American city. That has two big implications. The most obvious is that the threat to America itself grows larger - though this may be less significant than it seems at first sight.
That is because no North Korean leader could rationally decide to launch such an attack, in view of the absolute certainty that America would retaliate with a far more devastating nuclear counter-strike, leaving North Korea in ruins. That does not mean there is no risk at all to the US: an irrational decision or an accidental missile launch remains a possibility, just as it does with other nuclear powers.
But the more serious implications relate to Japan and South Korea.
They have felt reasonably secure from North Korean nuclear attack because they assumed America could deter Pyongyang by promising nuclear retaliation against the North for any attack on US allies.
A North Korean ICBM upsets that calculation, because it would allow North Korea to threaten a counter-retaliatory nuclear attack on US cities. Faced with that threat, America would be less likely to strike North Korea in retaliation for an attack on South Korea or Japan. So those countries must be left feeling less secure.
Their fear is not so much that the North would launch an outright nuclear attack, as that the threat of such an attack could be used by Pyongyang to force concessions from Tokyo or Seoul.
That must increase the incentives for both countries to build nuclear forces of their own to deter the North.
That worries Washington, especially because it would weaken their dependence on the US, and thus weaken America's leadership position in Asia. And in the long run that means a gain for China in its contest with America for leadership in Asia.
These are the real reasons that Washington sees North Korea's ICBM programme as so menacing.
But what can America do about it?
No one really expects sanctions to work. Senior US administration figures continue to talk about their hopes for a diplomatic solution, but there is little reason to hope that the North can be persuaded to abandon a programme in which it has invested so much, and which it plainly sees as being so vital to its own security.
So military action seems the only possible option. Senior US officials themselves acknowledge that there is no military solution which does not run a very high risk indeed of escalating into a major war on the Korean Peninsula costing hundreds of thousands of lives - or even more if nuclear weapons were used.
Nonetheless this is what President Trump has been threatening to unleash. If there has been any coherent policy rationale at all behind Mr Trump's vague and menacing threats of "fire and fury" against North Korea, it has been to try to convince Mr Kim that he is indeed determined to launch a major war to prevent North Korea achieving an ICBM capability.
Would he really do it?
That is not a remote question. All the evidence points towards the North being perhaps only a matter of months away from its goal. Any US attack on North Korea would obviously be much riskier for Washington once it has ICBMs. So if Mr Trump is going to stop North Korea he would have to act soon - which means striking North Korea hard the next time it conducts a test.
Of course Mr Trump hopes, and probably expects, that he will never face this choice, because his lurid threats will have already convinced Mr Kim to abandon the ICBM programme. If so, he will deserve credit for a notable piece of diplomatic brinkmanship.
But there is a real danger that Mr Kim will not be convinced. Mr Trump has a reputation already for not matching tough talk with action. His advisers clearly understand the immense costs and risks of military action. America's South Korean allies - whose agreement would be essential for any effective campaign to be launched -are unlikely to agree. China has hinted that it would stand by the North if the US attacks. And Mr Trump's own longstanding unwillingness to commit America to large-scale military commitments abroad is clear.
So there is a real chance that Mr Kim will decide that Mr Trump's threats are just a bluff, and that he will call that bluff by going ahead with another ICBM or nuclear test, perhaps quite soon.
If he does, then Mr Trump will face a truly harrowing choice between two very bad alternatives. No one can know which he will choose.
If he chooses to do no more than push for yet sterner condemnation and tougher sanctions, then he will be acknowledging that all his tough talk in recent weeks has been so much hot air. His credibility will be very badly damaged, and so will America's. And North Korea will proceed to build the weapons which will help to erode US leadership in Asia.
If he launches a military strike, he will turn Asia, and the world, upside down.
There is no good way out of this. The least bad way would be to recognise that we probably can't stop North Korea building ICBMs, and start working out how to live with this new danger as safely as possible. That requires a lot less tough and noisy talk, and a lot more quiet, hard thinking.
•Hugh White is professor of strategic studies at the Australian National University in Canberra.
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