If countries acted like rational players, the US would have eliminated the DPRK nuclear program as soon as it became known and the ROK would have invaded and conquered the DPRK just as soon as it became evident the PRC would not be drawn into the conflict. All of this would have occurred approximately circa 1990.
But countries are not rational actors. Their leaders have domestic political considerations and the nation-state system itself has a short memory. Any initiative by the US and ROK to head off the emerging threat of North Korea would have come with immediate costs to the decision-makers that outweighed the expected benefits of rational action. And so they kicked the can down the street giving just enough cover to their actions so not to appear as craven as they were. The DPRK intelligently indulged the US/ROK in this kabuki theater.
From the DPRK position, it would be suicidal to over-respond to a proportionate action by the US/ROK. Any artillery attack against Seoul would be met with annihilation of the barraging force and of the regime, if not with total conventional conquest by the South. The North knows this, yet it maintains the threat because it serves its purpose in holding the US/ROK at bay. The real fear of the US/ROK is not retaliation by the North for a preemptive strike, it is the appearance that the political leader who initiated the action is accountable for the DPRK's response rather than Kim. Kim postures himself so as to escape rational consequence, but meanwhile, his actions are very deliberately designed to achieve his intermediate goal of separating the US from the ROK. His propaganda makes this clear.
Is there a way for the US/ROK leaders to deal with this complication while achieving the purpose of denuclearization? Yes, they could assassinate Kim.
But countries are not rational actors. Their leaders have domestic political considerations and the nation-state system itself has a short memory. Any initiative by the US and ROK to head off the emerging threat of North Korea would have come with immediate costs to the decision-makers that outweighed the expected benefits of rational action. And so they kicked the can down the street giving just enough cover to their actions so not to appear as craven as they were. The DPRK intelligently indulged the US/ROK in this kabuki theater.
From the DPRK position, it would be suicidal to over-respond to a proportionate action by the US/ROK. Any artillery attack against Seoul would be met with annihilation of the barraging force and of the regime, if not with total conventional conquest by the South. The North knows this, yet it maintains the threat because it serves its purpose in holding the US/ROK at bay. The real fear of the US/ROK is not retaliation by the North for a preemptive strike, it is the appearance that the political leader who initiated the action is accountable for the DPRK's response rather than Kim. Kim postures himself so as to escape rational consequence, but meanwhile, his actions are very deliberately designed to achieve his intermediate goal of separating the US from the ROK. His propaganda makes this clear.
Is there a way for the US/ROK leaders to deal with this complication while achieving the purpose of denuclearization? Yes, they could assassinate Kim.