Keep calm.
It is as usual the antics of an IGNORED dictator, whom needs financial aid for its ailing country under his management.
If he truly wanted war, it would not be the island COASTS that would be targeted, It would be the capital city Seoul itself & every military installations in S, Korea.
His actions only shows that he does not want war, but only to be CONSULTED upon & his mismanagement of economy to be supported by Neville Chamberlin types to prevent war & his hold upon the country & poorly fed HUGE military.
The solution is:- rather than to live on knees to his half baked terrorists actions, WITH-HOLD any further FUNDING$, curtail EVERY INDIRECT means that N.Korea seeks to get funds such as thru online gambling, scams, etc. It would bring him & his overfed cronies to their knees instead, as they too, fear death...like every mortal.
He too knows WHAT war would bring to his regime - the end. Thus his use of terror as a PYSCHOLOGICAL weapon, proven his timidity to strike Seoul but instead only into unproblematic areas. His strategy is the only commonly used - kill the chicken to frighten the monkeys....sigh.. We know the regime only too well & their predicable behaviour....