Ok, so this seems to be real.
It's always difficult to tell when North Korea is making threatening statements, but U.S. and South Korean forces are now mobilizing on a large scale, as the linked article indicates. Three days ago, North Korea stated its abandonment of the armistice in place since 1953, so war is, from a legal standpoint, "on."
I am not thrilled at the prospect of U.S. involvement in a potential third land war in Asia. Nor am I enthused by China's continuing failure to rein in North Korea to the extent that it could - although it seems to have shifted its position ever so slightly today.
I did not realize that North Korean forces have killed over 100 members of the U.S. military since the Korean Conflict came to a stalemate by armistice in 1953:
Since the end of the Korean War in 1953, almost 400 South Korean and 100 U.S. service personnel have been killed in encounters with North Korean infiltrators, according to the U.S. Strategic Digest published last year.