Cumings is America's foremost historian on Korea in the modern era. (read the above Wikipedia link) As such he knows of what he writes about North Korea in this article which provides details about their weapons program in recent decades in relation to US concerns.
North Korea is the only country in the world to have been systematically blackmailed by US nuclear weapons going back to the 1950s, when hundreds of nukes were installed in South Korea. I have written much about this in these pages and in the "Bulletin of the Atomic Scientists". Why on earth would Pyongyang not seek a nuclear deterrent? But this crucial background doesn’t enter mainstream American discourse. History doesn’t matter, until it does—when it rears up and smacks you in the face.For a much needed (for Americans) full history of US-Korean history of relations, I highly recommend that you read at least volume 1 of Cumings' 2 volume book entitled The Origins of the Korean War.