1) Kim is a fascist who wants to re-unify the Korean Peninsula under his control.

2) Kim has made an irrational investment in WMDs to accomplish  #1.  He wants to use his investment.

3) Kim is a lunatic who believes that he is a living deity, sui generis immune from an US retaliatory strike.

4) Kim holds the US responsible for protecting the Japanese who had a brutal occupation of Korea c. 1910 - 45 which killed and raped millions of Koreans;  he hates the US because of US carpet & napalm bombing during the Korean War which killed hundreds of thousands of civilians and decimated the North Korean infrastructure.

5) Kim believes in the racial superiority of Koreans and believes that they are destined to rule the world.

6) Kim is a psychopath who has no problem whatsoever murdering anyone or millions if he believes that it will help to attain his geo-political goals.

7) Kim has repeatedly told his people that he will nuke the US;  to maintain his credibility he must do so.

Got it?