LH,

Like Iraq, the US ( actually, the UN) is presently at war with North Korea- with a cease-fire in place based on certain behaviour by both parties. When one side violates the agreed upon behaviour, this will always bring the threat of active military conflict into consideration.

Note this is JAPAN that is considering direct military action, NOT the US. They just want to figure out if their constitution, forced on them by the US after WW II, allows for it.