Why Is North Korea Starting a Crisis Now?

Something is going on in the North that is, as yet, invisible to outside observers. Remember that Kim Jong-un disappeared for three weeks in April-May, and has only rarely been seen since. His sister, Kim Yo-jong, has suddenly taken on a much more prominent—and much more militant—role in governing the country, even apparently taking it upon herself to issue orders to the military in her own name. Is brother Kim sick? Is sister Kim taking over the family business?