This is all to preface a simple, grim possibility. North Korea, a totalitarian dictatorship and the only country to test nuclear warheads this century, might only be five or so years away from building working, nuclear-tipped ICMBs of their own.

The New York Times reports:

Military experts say that by 2020, Pyongyang will most likely have the skills to make a reliable intercontinental ballistic missile topped by a nuclear warhead. They also expect that by then North Korea may have accumulated enough nuclear material to build up to 100 warheads.

Siegfried S. Hecker, a Stanford professor who has traveled to North Korea and who formerly directed the Los Alamos weapons lab in New Mexico, the birthplace of the atomic bomb, said North Korea's progress in missile and nuclear development signals that it has gone from seeing unconventional weapons as bargaining chips to “deciding they need a nuclear weapons fighting force.”

The Pentagon warned Congress in a report earlier this year that one of Pyongyang's latest missiles, if perfected, “would be capable of reaching much of the continental United States.”

North Korea does not yet have the ability to launch a nuclear-tipped missile against targets in the mainland United States. What they have right now are missiles--some that appear to work--and nuclear warheads, which may or may not fit on top of those missiles. Pyongyang still has work to do to prove that this is a real threat. Yet that work, it appears, is getting done. Just last week, North Korea tested another nuclear warhead. August's successful submarine missile launch followed a series of earlier, unsuccessful tests starting in December 2015.

This is not new science, and it doesn't take unknown discoveries to make it happen. ICBMs are a solved problem, and North Korea is iterating its way to an answer.