Who’s In Charge
The BBC has an article that indicates that the South Korean intel believes that the North Korean activity is about naming a successor.
Kim Jong-Il had a stroke, and has not formally named an heir, which makes the people at the top of the North Korean power structure nervous. The South Korean intel people apparently believe that all of the recent belligerent activity is for internal consumption, to confirm that he is still in charge, and to anoint his successor.
Following a custom, Kim Jong-il has three sons all named Kim Jong with the suffixes -nam, -chul, and -un. He has apparently selected the youngest, Kim Jong-un, to be his heir. This may be a difficult sell to the tradition-minded military, and the reason for all of the war-like behavior.
