Based on an answer submitted on Quora
Trump accomplished nothing in North Korea, just as with his various trade wars, because he tried only threats and bullying but no quid quo pro that might actually tempt the other side into a deal. Therefore North Korea still has nuclear weapons at the end of the Trump term. In fact, its nuclear and missile program is farther along than when Trump took office.
In order to know how to deal with North Korea, it is important to think about why North Korean leaders have gone to great expense in a relatively small and poor country to develop nuclear weapons in the first place. It is because North Korean leaders see America’s leaders overthrowing the leaders of countries they don’t like, including Saddam Hussein in Iraq and Muammar Gaddafi in Libya. Knowing they are hated by the US as well, the North Korean leaders see nuclear weapons as insurance against being removed militarily. North Korea cannot hope to compete with the US in conventional military force, but even a small nuclear deterrent might secure its regime against overthrow by the US.
Therefore, logically, if the US wants North Korea to make a deal to eliminate its nuclear weapons, which was Trump’s stated goal, then it would be necessary to reassure North Korean president Kim Jong Un with concessions that would make his regime feel secure. If you do not offer such concessions, then of course he may talk politely to the US for a time, but it all means nothing, because he will keep his nuclear insurance to stay in power. He has no wish to commit suicide by disarming merely under feeble economic pressure. Trump threatened military action, but North Korea called his bluff by threatening right back, so Trump tried diplomacy instead, but offered far too little to secure a deal.
Like Nixon in China, Trump had more potential to cut a deal with North Korea, because unlike his Democratic predecessor, Obama, he would not have the Republicans in Congress attacking any deal he might try to make. However, for lack of imagination or determination to do anything more than grandstanding, Trump offered little of substance. One thing he did do is stop certain US-South Korean military exercises in return for North Korea stopping nuclear and missile tests, but that was far too little to achieve a comprehensive settlement.
Based on my own discussions with South Korean government officials and diplomats, plus North Korea’s public statements, I believe North Korea is looking for several things in return for giving up nuclear weapons, at least: 1) a formal peace treaty ending the Korean War; 2) full diplomatic recognition by the USA of the North Korean regime; 3) opening of normal trading relations with the rest of the world; 4) withdraw of US forces and nuclear weapons from South Korea; 5) some degree of conventional arms limitation between the two Korean governments so that North Korea can afford to spend more on economic development and less on arms; and 6) confidence-building measures to reassure both sides that no surprise attack can be launched, perhaps involving peacekeeping forces on the border among other things. North Korea devotes a higher portion of its economy to armed forces than any other country, because it is half the population and much poorer than its South Korean neighbor. Without the assurance of security and the possibility of economic development, North Korea would be vulnerable, according to the fears of its leaders, if it surrendered its trump card: nuclear weapons.
The problem is that any American leader making such a comprehensive settlement with North Korea would face domestic political opposition, particularly any Democrat. This would be a little like Egyptian President Sadat’s bold gesture toward peace with Israel, for which Sadat was assassinated by domestic foes. Giving up too much for peace without security or prosperity is dangerous for any leader of a small country. Trump’s gestures were not backed by substantive policy changes, so the North Koreans eventually learned that Trump’s words were empty, and they clung to their nuclear arsenal instead.