And North Korea also prepares for war, which might not be such a strange thing as you have actually threatened them with nukes. But it means even though they agree in principle to draw back troops from the DMZ neither side does! SK has as many troops as under the military dictatorship. Found ways to go around producing long range missile (i.e. by building cruise missiles with similar range and for the same kind of targets) which they have agreed not too (NK aren't bound by that, they are by un resolutions though). And so on. Yet South Korea can blame the situation on the North as they can always bring up that they haven't decreased the number of their military.
from the article: U.S., South Korea navy drill resumes amid North Korea's nuclear threarts