I love how all the people personally attacking me have no counterargument. Can you answer YES to any of these questions?
Will North Korea voluntarily give up is nuclear capability?
Will the United States accept a North Korea with nuclear capability?
If the United States launches a massive attack on North Korea, will they hold back from nuclear retaliation?
Unless you can answer YES to one of these questions, nuclear war will happen. All the people saying the chance is less than 15-20% are saying that the 'Yes' answers above add up to 80-85%. You would have to be as high as a kite to take that view, since there is currently zero evidence that any of the questions add up to Yes.
The closest is question 2, since at least some US experts believe this is necessary. That's why it's the position I advocate.
You're missing what is probably the most important question between two and three:
Will the United States respond to a North Korea with nuclear capacity by launching a massive attack?
To which the answer is and has been an easy no for over a decade, putting no far above 95%. I'm sure there are other missing questions to, but they don't immediately spring to mind.