The USA wants it to happen. If a war erupts... the casualties will be borne by S. Korea, who will eventually win the day, ...and the USA will be right up China's butt. Right now N. Korea is the buffer zone. Allow an attack to occur, ...there goes the buffer zone.
As for Guam, Japan, or any other US base in the line of fire... I really don't think the military strategists care about lost American lives. If they did, ...they wouldn't be supplying avowed enemies of the USA with weapons, training, and financing, and they wouldn't be so inclined to provocation, or sending soldiers into harms way.
