if the USA removed it's large number of forces out of the area the tensions might ease...just saying.

North Korea already has the bomb, in spite of billions already surrendered as aid! And they could be assisting the Iranians, with their nuclear ambitions?
Clearly this tack isn't working and needs to be replaced with a no cooperation no aid strategy.
As harsh as this might be on already starving North Koreans, their conditions could hardly be worsened, by cutting off the very lifeline, that is all that keeps this warmongering sabre rattling administration in power!
Rhrosty.

Quite a range of suggestions - superimposing German experience on the rather different conditions of the Korean Peninsula.

I don't know where the authors get "Some experts argue, small, two to four kilogram warheads". Such sizes simply may not achieve critical mass or may deliver too small an explosion - not worth the nuclear retaliation of much more powerful US weapons.

One difference is-was that the Soviet Union and East Germany were understandable and ultimately rational regimes that believed in Mutually Assured Destruction. In contrast North Korea is an updated dynastic (Kim) feudal entity which is unpredictable - with the Kim in power perhaps considering sacrificing his fiefdom:

The authors' suggestion below risks a nuclear response from North Korea:

"The U.S. President must make clear now: If North Korea dares to ignore this red line, there will be no other outcome than a preventive airstrike by the U.S., which would target all his leadership structures, as well as the leader himself. For the first time during the U.S.-Korean military consultations in early October 2013, U.S. Secretary of Defense Chuck Hagel officially agreed that a pre-emptive strike against the North is legitimate and necessary before a nuclear weapons capability is achieved."

Details of the results of North Korea's third nuclear test have not indicated the degree of weaponization of that country's nuclear capability. If North Korean nuclear devices are currently too large for traditional aircraft or missile delivery there are terrestrial or naval means of delivery - something South Koreans would be worried about.