Your talking about Nuclear War. One nuke launched and it would instantly escalate. Does not matter who launches first there will be devastation in N.K., S.K., Japan and this is just a guess but there would be a nuke landing in the middle of the American fleet off the coast of Korea, not to mention the 15000 or so military personnel in S.K.. That would just be the start of it, you would then have nuclear radiation moving across most of S.E.Asia in the water, in the air and most of Japan and all of Korea would be unlivable.
The cost of launching one Nuke is devastation that will last for 50 years.
My guess is if you see US military personnel moving out of S.K and the US fleet pulling back that to me would be a sign of a first strike. That is the standard procedure for a nuclear strike, move your assets out of harms way.
Then there is the question of China.
If there is Nuclear war is Asia then Australia will be affected as well.
