I am not worried because I did the research.  JFK's "full retaliatory response: thing regarding Cuba.  So I looked at a map of the region, and then checked the weather in the region.  Only three nukes required to retaliate.  One for Kim's crib. One more for NE Korea and Russia loses the use of Vladivostok for a few thousand years.  One near the Yalu river "dip" and China loses the use of a few/many hundreds of square miles of their country for a few thousand years.  Castro did not want Cuba turned into a parking lot.  I suspect Russia and China know how to read maps.  I am not sure about Kim's character but I doubt he wants to be the last of the dear dynasty.