Author bought all the Pentagon BS about NK. Here's my no BS take:

1. NK is enemy of no one in the world except the U.S. Not friend of SK, Japan, but not enemy. There is a good reason why NK has been and will be enemy of the U.S. for another century. The U.S., for no reason other than incompatible ideology, invaded Korea in 1951 and killed 3 millions in North Korea. NK did not drop a single bomb on the U.S. for the same reason. For this Holocaust, NK like Vietnam & Cambodia will be enemy of America for a very long time. 
2. Given their enemy status NK development of big missiles, nuke ICBM even, is a very sound strategy. The sole purpose is to discourage another U.S. invasion, and if that happen retaliation. NK adopted this strategy from China, which has worked most effectively. When U.S. threatened nuke and invasion of China during the Vietnam War, China did a crash program for nuke and ICBM. U.S. dared not touch China since. 
3. China needs NK to counter U.S. military encirclement.