It's not even fear mongering really at this point. It's good old fashioned sabre-rattling. You can always trust that North Korea will continually threaten the US and its allies periodically. It's like clockwork. They need to do this in order to maintain the level of tension to keep their people in line and to keep the people from around the world to be looking at them constantly. It's also done so that they can showcase their power; much like an army goosestep through the streets, but for the international audience.
Sabre rattling is done by everybody. The US constantly has military exercise near or around their enemies' territories, Russia often habitually trespasses into UK airspace to test their response times, and so on.