It seems possible that plans are already being implemented to invade North Korea. I am not speaking of contingency plans; I am speaking of a date certain, a definite schedule, with step number one being the recent flyover of B1-B bombers near the North Korean border. I am not, of course, privy to any such information, but President Trump seemed supremely confident when he made his assurances that (inexact quote) "we will handle North Korea."
The reason for all this is that the Norks (as the North Koreans are informally referred to in military parlance) have nuclear weapons and intercontinental ballistic missiles (ICBMs), which pose as close to a clear and present danger as we dare to allow without taking decisive, pre-emptive action – immediately.
The only constraint now is feasibility. Are we able to attack and win? Can we accept the consequences of action versus those of inaction?
The consequences might be cataclysmic. North Korea reputedly has thousands of artillery guns in caves, within firing range of Seoul, the capital city of South Korea. Seoul is a huge metropolis with some eight million or more inhabitants. I've been there, and it is easily comparable to most large American cities. Those artillery weapons can be expected to deploy within minutes, to fire an overwhelming barrage, and to kill as many as a million people within the first hour of a major war. There can be no doubt that the Norks would do this in the first moment they perceived an existential threat.