There are 2 nations in the world that simply don't care about American threats and one of them is North Korea. The other is Iran.
Kim Jong Un doesn't care because he's a typical insular 3rd world dictator. As far as he's concerned, there is no NK without him. He knows he can't win but would allow every last man woman and child die first. Despite the fact that he'll lose he can still inflict massive casualties in South Korea before its over.
The 12ers who run the show in Iran are even worse since they want Armageddon.