The possibility of miscalculation or misinterpretation: Note this by S. Korea's President Moon (from this article) North Korea appears to be inches away from the “red line,” which President Moon Jae-in defined as being capable of developing nuclear intercontinental ballistic missiles.
and then also: http://www.businessinsider.com/south-korean-moon-massive-punishment-north-korea-crosses-the-line-2017-8
Kimmy might not strike 1st at Seoul or Guam, but he may think Moon or Trump will allow that capability - and maybe they will not.
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The possibility of mistake: Such as a North Korean test that goes off course and hits / nearly hits Japan or a US ship.
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Iranian / N. Korean cooperation.
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Racial hatreds in S.E. Asia. They may be now kept for the most part under a carefully maintained and polished veneer, largely for business reasons, but, a veneer it often is.
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Long term risks of a nuclear arms races in S.E. Asia and / or the ME. (See also "cooperation" above.)
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Chinese "use" of North Korea. (There are many possibilities here, and, no, I don't think the Chinese are above sacrificing millions of North Koreans to advance their own interests, especially if they think they can blame the US.)
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The possibility (approaching probability with time) of "Murphy's Law" enforcing itself. Does N. Korea have the sorts of internal "Fail Safe's" the US and Russia do? What if a North Korean General decides, rationally or not, to hit back @ the Kim dynasty after a friend or family member gets offed, and further thinks that while he cannot kill Kim himself, he can create an "incident" (say, a WMD strike on Seoul) that will bring down the Kims?
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The small but finite possibility Kim might make an irrational decision at some point. Recall, until short weeks ago, it appears that anyone one might ask about Stephen Paddock's rationality or decency would respond positively. Kim CLEARLY has not decency - he is vicious, and evil, and while "rational", one wonders what his brand of rationality does to a human brain with time.
Agghh. “race”, not “races”.
“Does N. Korea have the sorts of internal “Fail Safe’s” the US and Russia do?”
I wouldn’t be as dependent on “fail safes”. For example, a man named Stanislav Petrov who died just last month:
http://bit.ly/2z4Nrcy
Also not quite fail safe;
http://ti.me/13ohlbv
Whatever option/route the US takes on NK, it’s wise to keep Murphy’s Law in mind.