NK can kill nearly all Americans right now with:

1) EMP attacks 

2) Biological weapons -- e.g. smallpox -- released in cities

3) Nukes smuggled in containers and/or launched from subs, freighters, satellites

4) Cyber attacks that destroy the grid.

Especially if 1),2),3), 4) are coordinated.

China & Russia pay lip service to sanctions, but they do not enforce them.  They provide NK with technology, money laundering, and work for NK slave labor.

China is trying to steal most of the South China Sea to control key sea lanes and natural resources. NK diverts attention from
this theft.

Iran, Syria & Pakistan are also NK allies.

Kim is a murderous psychopath who has reason to hate the US & Japan which he daily threatens to annihilate.

Hence the US & Allies must devise a viable scheme to kill Kim.  It is not a perfect solution, but  it is the best solution.

Otherwise Kim will continue to develop better WMDs & delivery systems.

And he will use them against U.S. Allies and the U.S.