And even without the factional struggles and insane personality cults, the DPRK's position is that the US is the real enemy preventing unification with their so

And even without the factional struggles and insane personality cults, the DPRK's position is that the US is the real enemy preventing unification with their southern neighbour. For both ideological and strategic reasons, any country wants the capacity be able to threaten their real enemy, not just their immediate neighbour, especially if that neighbour is - according to their political theory - a kindred nation under the yoke of the hated enemy. Missile threats to the US probably irritate their tacit Chinese allies less than missile threats on the Korean peninsula too...