The phrase "common sense" implies practical and prudent good judgment, with a further implication that the obviousness of common sense is "common" because it is shared by many or even all. For example, 122 nations just signed a Treaty on Nuclear Prohibition, confirming a majority planetary common sense that these weapons have become dangerously obsolete as a foundation for international security.
North Korea and the United States do not appear to share much of a common sense about anything with each other. Evan Osnos of the New Yorker has written a concise and intelligent summation of our mutual bewilderment and paranoia that should be required reading for the U.S. military-diplomatic-political leadership.
Given that the Korean War was never genuinely resolved so long ago, substantive reasons for conflict remain. But the destruction of both Koreas by further war would be all the more tragic and absurd if it happened less from misguided attempts at resolution by military means than from the present complete lack of communication, a lack that includes ignorance and puzzlement in North Korea about US politics, historical amnesia in the US ("the forgotten war"), and destabilizing brinksmanship bluster on both sides.
It is no harder to grasp the historical causes of North Korea’s paranoia than it is to understand our own fears: Korea was invaded and brutally colonized by the Japanese from 1910 to 1945.
At the end of World War II, the victorious Americans and Soviets divided the country into two separate zones of occupation. No agreement ever ensued as to where the capital of a unified Korea should be. When the North attacked the South in 1950 in a forced attempt at reunification, the Americans came in one side and the Chinese on the other.
Military stalemate followed three years of a war that included the deaths of a million Chinese soldiers, more than 400,000 North Korean soldiers and 600,000 civilians, and almost 100,000 Americans. Our air force bombed and napalmed the North until there was no intact target left, a shattering level of devastation not forgotten by North Koreans to this day. The aim of the North ever since has been to avoid a repeat of such helplessness, and the major means of avoidance became the acquisition of a credible nuclear deterrent – ironically ensuring that war in Korea today would be far worse than in 1950.
Meanwhile, in order to protect its ally below the 38th parallel from invasion, the United States surrounds North Korea with ships, flies along its airspace with bombers, and conducts military exercises that are seen by the North as highly provocative – just as the US would see red if similar massive shows of force were conducted so close to our own coasts and up and down the edges of our own airspace.
The philosophy of nuclear deterrence pursued by both sides is all about credible threats, which drown common sense in an ocean of anxiety. The philosophers call this a performative contradiction: the weapons are there to prevent their use by anybody, but the threat of their being used must be seen by all as real, which means they must be instantly at the ready, which cuts the margin for error in crisis, which can lead to mistakes etc. etc. When will the experts see how there is no good way out of this death spiral waiting to happen?
Additionally, credibility requires not only that threats be credible to one adversary, but intended as a warning to all. This was the catastrophe of Vietnam in a nutshell, where the US could not afford to be perceived by the Soviets as weak, so it fought, and lost, a futile proxy war.
Therefore the ultimate resolution of the North Korean challenge must include a total shift in paradigm on the part of the US away from the credibility of deterrence to the credibility of gestures of good will, such as a solemn pledge of no first use, in all potentially nuclear conflicts around the globe. The United States must cease to obstruct, and instead encourage, a grand plan of verifiable, reciprocal global denuclearization.
In the long term it is a virtuous circle of nuclear disarmament that will most effectively undercut North Korean motives for its own destabilizing nuclear gestures. Kim Jung Un’s regime will not last forever in its present form. If the US could contain the Soviet Union through a half-century of Cold War, we can cooperate with the world community to contain a small, impoverished nation and await its inevitable transformation.
Meanwhile, we need to talk with them! The first "common" sense North Korea and the United States presumably share is a desire to survive. To strengthen the shared common sense that possession of nuclear weapons is a probable cause of the eventual use of nuclear weapons requires slowly nurtured relationships and a ratcheting down of the rhetoric of threat.
While there is international agreement that Kim Jung UN is worthy of collective sanction, it doesn’t hurt to remember how many countries feel that the United States itself is dangerously militaristic, and further that we have not lived up to our obligations under the Nuclear Non-Proliferation Treaty of 1970 to make good-faith efforts to cut and finally eliminate our arsenal. Part of getting North Korea to change includes realizing that we have to change. Without weakening ourselves, we can initiate diplomatic feelers that could lead to threat reduction on both sides. We can build trust on the basis of a shared interest in survival – not capitulating to each other but capitulating, like those other 122 nations, to the common sense that nuclear weapons have no constructive use.