This article shows underground tunnel that was built during 1970's from the North Korea. Most of the tunnels were to be used to transport armies or spies into South, most likely to Seoul. This article provides detailed information and pictures. So I think it's interesting to see how North Korea is active in terms of aggression against South Korea. In the book we are reading for the class, I remember one part where North Korean official told the author that they don't have any intension to attack South Korea, but only to unify peacefully (and, of course, U.S is ‘disrupting’ the peaceful unification). I don't think building an underground tunnel isn't very "peaceful," especially when the tunnel was to be used for military and guerilla tactics.