An analogy could be the DOS, denial of service, action on the internet. Interrupting trade is an act of war, just as DOS is a crime. Recall the Arab embargo of oil to the West was an act of war. Also, a Declaration of War is an act by Congress in this country, although other countries may have their own interpretation. In the case of N Kor, as far as they are concerned, whatever they say is a declaration of war is a declaration of war.
Pre-World War II Japan considered suspension of scrap metal shipments to Japan an act of war; not a judgement, just information.
Right Whale.......I think Iran is more of a threat; I would be most interested hearing your opinion on that subjecct.