If N. Korea crossed the parallel their casualties would far outway our own. We have a fleet less than 30 miles off shore. However, I highly doubt China will let that happen. N. Korea gets nearly all of their food, oil, etc...everything they need for survival from China. If China tightens the noose N. Korea will back down. That is unless Kim jong forgets his meds and starts dancing on his ICBM launch button.