The US Military Joint Chiefs of Staff (of course) have plans
ready in place for war against North Korea, if and when necessary.
The following (article linked below) are 3 broad options for US
military action against North Korea, but all of the 3 military
action plans face a common set of problems that are both essential
to overcome and, so far, have proved insurmountable.
For all of the United States’ military superiority, North Korea
has one significant advantage : its willingness to accept risk.
This allows the country to retaliate against any limited strikes by
imposing costs that are disproportionately unacceptable for its
adversaries to bear.
Even if the US Military can easily kill 99% of all North
Koreans, the US populace will find absolutely unacceptable the loss
of life in the tens of thousands of US citizens, let alone the
millions that are almost certain to die, as long as just one of
North Korea's many nuclear missiles successfully make it to USA,
which will almost certainly happen (because once an
intercontinental nuclear missile is launched, the chances of
successful missile interception are very low, even with THAAD, and
North Korea will certainly launch *dozens* if not *hundreds* of
nuclear missiles simultaneously, at the start of any actual
war).
The Risks of Pre-emptive Strikes Against North Korea
https://www.nytimes.com/2017/03/18/world/asia/us-north-korea-weapons.html?_r=0
