George Friedman makes a very interesting point.
The US had little to gain from a war with North Korea; it wanted only to destroy the North’s nuclear program. The war plan was complex, and though it was likely to succeed, “likely” is not a term you want to use in war. North Korea’s nuclear and missile facilities were scattered in numerous locations, and many were underground or in hardened sites. And the North Koreans had massed artillery along their southwestern border, within easy range of Seoul. In the event of an American attack on North Korean facilities, it was assumed those guns would open up, killing many South Koreans. Destroying those batteries would require a significant air campaign, and in the meantime, North Korean artillery would be firing at the South.
The US turned to China to negotiate a solution. The Chinese failed. In my view, the Chinese would not be terribly upset to see the US dragged into a war that would weaken Washington if it lost, and would cause massive casualties on all sides if it won. Leaving that question aside, the North Koreans felt they had to have nuclear weapons to deter American steps to destabilize Pyongyang. But the risk of an American attack, however difficult, had to have made them very nervous, even if they were going to go for broke in developing a nuclear capability.
But they didn’t seem very nervous. They seemed to be acting as if they had no fear of a war breaking out. It wasn’t just the many photos of Kim Jong Un smiling that gave this impression. It was that the North Koreans moved forward with their program regardless of American and possible Chinese pressure.
Another Player Enters the Game
A couple of weeks ago, the reason for their confidence became evident. First, US President Donald Trump tweeted a message to the South Koreans accusing them of appeasement. In response, the South Koreans released a statement saying South Korea’s top interest was to ensure that it would never again experience the devastation it endured during the Korean War. From South Korea’s perspective, artillery fire exchanges that might hit Seoul had to be avoided. Given the choice between a major war to end the North’s nuclear program and accepting a North Korea armed with nuclear weapons, South Korea would choose the latter.
With that policy made public, and Trump’s criticism of it on the table, the entire game changed its form. The situation had been viewed as a two-player game, with North Korea rushing to build a deterrent, and the US looking for the right moment to attack. But it was actually a three-player game, in which the major dispute was between South Korea and the United States.
The US could have attacked the North without South Korea’s agreement, but it would have been substantially more difficult. The US has a large number of fighter jets and about 40,000 troops based in the South. South Korean airspace would be needed as well. If Seoul refused to cooperate, the US would be facing two hostile powers, and would possibly push the North and the South together. Washington would be blamed for the inevitable casualties in Seoul. The risk of failure would pyramid.
There's more at the link. It's well worth your time to read the article in full.
This explains, to my mind, why the US response to North Korea's undoubtedly aggressive moves has been so muted. There is no doubt that the USA could turn the whole of North Korea into a radioactive desert - but that would poison parts of China and most of South Korea with fallout, which neither country will accept. Short of such an all-out nuclear attack, any US military intervention in North Korea must inevitably involve South Korea. If South Korea is not willing to permit its territory, or its airspace, or its waters, to be used for that purpose, the USA is effectively stymied.
I see only one way to break the logjam, and force the issue. That would be for the USA to announce that, in view of North Korea's aggressive actions and stated intentions to become a nuclear power, it is willing to sell nuclear weapons to Japan and South Korea. Note that I said "sell" - in other words, not station US nuclear weapons in those countries under US control, but give each country its own nuclear warheads and delivery systems, under its own sovereign control. China would instantly have kittens - a nuclear-armed Japan must be close to its worst nightmare, and a nuclear South Korea wouldn't be far behind that. If anything could force China to rein in the North Korean regime, that might do it.
Frankly, I see no other way of breaking the stalemate over North Korea. Can readers suggest anything better?