North Korea is a dictatorship. The country is run by a single family which brooks no dissent. It ha,s with Chinese help, built up a small nuclear deterrent that can strike at South Korea and perhaps Japan. There was a time when the North had no nuclear weapons and it was known to the USA that it was developing them. In 1994 the then president Bill Clinton thought of a pre-emptive strike on the North. The attack was however not carried out as an assessment revealed that the North would unleash a barrage of artillery gun fire on Seoul which is just 15-20 miles from the Line of Control.
The Pentagon came to the conclusion that a million lives would be affected even in a limited action. At that time the North did not have nuclear weapons.
The stakes are more heavily stacked against a military adventure now, as the North under Kim Jong has some rudimentary nuclear strike capability. President Obama wanted to tighten the economic screws on the North, but china was not enthusiastic. President Trump has realized the hard way that a strike on the north will not lead to any solution. The South Korean government is also not enthusiastic about a strike and would like a negotiated settlement.The front-runner in the coming election, Moon Jae-in, wants direct contact with the north. It knows the terrible calamity that will befall The South whose major centers of population lie close to the DMZ.
This has been the dilemma for all presidents.
China's demands
Donald has tried to overwhelm Chinese president Xi into supporting action against the North but the Chinese want two things before they act. They want the removal of US nuclear weapons from South Korea and the dismantling of the THAAD anti-missile system. That is the reason the US secretary of state Rex Tillerson in a speech, has called for direct negotiations with North Korea with the aim of removing nuclear weapons from the North.
He was careful not to mention the word "denuclearization". In he had used this word it would also mean the removal of the nuclear weapons stored in the South. China also wants the annual military exercise near the north to be discontinued.
The other side
The US and perhaps Donald is aware that a North Korean artillery barrage on Seoul would have a catastrophic effect.
It could lead to over 100,000 casualties within a few hours. The THAAD system may not be much of a defense against an artillery attack. Trump, therefore, is realizing the hard way that a strike on the North is not easy. The western press is talking about refugees from the north, but hardly anybody is talking of the millions who will die and lose their homes and livelihood in the South. Where will they go?