I think the extent to which North Korea engages in externally-oriented violence depends on the extent to which Kim Jong-un feels that he needs to prove himself to solidify his rule.
http://www.nytimes.com/2011/12/19/world/asia/kim-jong-il-is-dead.html
http://www.nytimes.com/2011/12/20/world/asia/china-moves-to-ensure-stability-in-north-korea.html