Trump is doing this because of the ICBM range improvement North Korea developed during the G. W. Bush and Obama Administrations.  

Sixteen years of ignoring the problem hasn't worked out too well.

One of the problems of being an ostrich is what happens to your rear while you have your head buried in the sand.

Saying the entire crisis is Trump's fault since he has only been there six months is bogus.

The only treaties I can find are about strategic nuclear weapons, not the tactical ones.  And those haven't been signed by all those with nuclear weapons.

https://en.wikipedia.org/wiki/Tactical_nuclear_weapon