A nuclear war has become unimaginable in the twenty-first century. The scale of destruction which a nuclear war will bring would blank our mind. The non-use of nuclear weapons on any country since Hiroshima and Nagasaki remains a significant phenomenon.The possible causes of non-use of the US nuclear weapons on North Korea are as follows:
Nuclear Taboo: Nuclear taboo is an informal prohibition of the use of nuclear weapons due to normative, moral, practical and diplomatic causes. It has played a significant role in preventing a nuclear use on North Korea and other adversaries. Though nuclear taboo is instrumental in discouraging nuclear war till now; it will not be enough to prevent nuclear war in the future.
International Opinion: the International community will go against any kind of nuclear use on any country including North Korea. The international community will deplore and denounce the use of nuclear weapons on North Korea.
Fear of Abandonment: The is a possibility that close allies especially, Germany, France, United Kingdom, Canada, Turkey and others would ostracize and abandon the United States. If it happens, Washington’s influence in Europe and elsewhere would be reduced significantly.
Damage to American Soft Power: There are two kinds of powers — hard power and soft power. Hard power is military capability and economic sanction. Soft power is someone’s ability of attraction and persuasion. American use of nuclear weapons would be a gross violation of human rights and international norms, which will severely damage American soft power.
Human Rights: the Nuclear weapon is a kind of Weapons of Mass Destruction (WMD) which does not differentiate between combatants and civilians. The use of nuclear weapons would grossly violate human rights. The United States is the pioneer and promoter of human rights and other liberal values. If the US itself violates those values using atomic weapons, then everyone would think of the United States as a hypocrite. So, human rights is a major factor behind the non-use of the US nuclear weapons on DPRK.
The proliferation of Nuclear Weapons: Any use of nukes would trigger a new wave of proliferation. Many states will seek to acquire atomic bombs to deter potential nuclear aggressors, as nuclear weapons are the ultimate deterrence against such an attack. The proliferation of nukes is not in the best interest of the United States. Washington has been combating the proliferation since the beginning of the nuclear age.
North Korean Nuclear Dereference: Pyongyang’s nuclear program is aimed at deterring the United States from dropping nuclear weapons on them. If deterrence fails, they will try to use those bombs against South Korea. Though Pyongyang’s nuclear weapons are still primitive and nearly unmountable on missiles, it can cause considerable damage, radiation, panic, and chaos in Seoul, if North Korea somehow manage to push them through the DMZ. This kind of scenario will discourage the United States from dropping nuclear weapons on the North.
South Korea will oppose: South Korean capital Seoul is only 35 miles away from the North Korean border. If the United States drops nuclear weapons on North Korea, South Korea will suffer too from radiation and nuclear fallout. So, South Korea will not like the idea of nuking Pyongyang.
Chinese Border: The Chinese city of Dandong is only 100 miles from the North Korean border. Radiation and nuclear material would affect those who live in that city.
The likelihood of deliberately using of nuclear weapons has been diminished as the nuclear taboo and other consequences of using nuclear weapons became central to the foreign policy experts, think-tanks and academic thinkers.