What is in it for them (the Korean)? If that question cannot be answered rationally, pondering such an action is ridiculous. Japan's strategic goal was to take the western world out of its "sphere" of influence and then establish a status quo, they were hoping that Hitler would be stronger and dominate Europe and thus not allow us to mount a sizeable counter offensive. They were wrong, but at least, they had a "valid" strategic goal, though with a very low probability of achieving it.