The US supports democratic regimes in the region -- e.g. Japan & SK.

It's difficult to know what to make of Trump's behavior.  Standard diplomatic behavior hasn't worked with NK.  Trump has made significant progress with the PRC;  he gets along well with both Abe & Moon.  But, do his jibes made against the known psychotic, Kim, who has WMDs  and is quite willing to murder anyone who threatens him, really helping matters?

Moon changed his mind and accepted the full deployment of THAAD after Kim continued to test missiles last summer.

The PRC & NK have very strained relations, especially since Xi has just cut off banking facilities for NK, cut oil exports, banned NK textile & seafood exportsand has sent 30K NK workers home.

War now would be a complete disaster.

A war later when Kim has hundreds of thermonuclear ICBMs might be an even greater disaster.

As Sartre would say: "Il n'y a pas de sortie."