The hostility is only between N Korea and S Korea/U.S. Hardly constitute 'the world'. The hostility is continuation of the Korean war. That war started when U.S. refused to return Japan colony Korea from defeated Japan as full sovereign. Instead the U.S. wanted the same arrangement as with western Europe, Japan, Philippines where It install military bases for control of country governments. All agreed because they were defeated and no choice. But Korea was not defeated by the U.S. and refused. When the U.S. imposed its military 'solution' anyway in the southern part of Korea the north rebelled. This is the origin of the Korean war and to this day the same contentious issue stops peaceful unification.