Members of the U.S. and South Korean air forces hed joint drills on April 20, a training event codenamed Max Thunder. But in the eyes of an increasingly hostile North Korea, scenes like these amount to one thing: preparation for an invasion. Pyongyang isn't taking any show of force by it enemies lightly, state media warning America of a "super-massive preemptive strike" that would wipe out the U.S., accompanied by the blunt message "don't mess with us."