Since 1945 the United States has not used nuclear weapons to attack other states, yet it has used nuclear coercion more actively than any state. Why did the U.S. use nuclear coercion at all against weak states or for non-vital national interests when the U.S. had superior conventional forces? What would have induced U.S. leaders to employ nuclear coercion? Nuclear deterrence theory and nuclear taboo theory cannot adequately explain why, under similar security and domestic environments, Dwight Eisenhower and Richard Nixon were more willing to use nuclear coercion whereas other leaders like Lyndon Johnson overall abstained from using nuclear threats. I argue that while U.S. leaders’ learning of the overly destructive damages of military nuclear use raised the threshold of using nuclear weapons to attack, the lack of learning or biased learning of the repercussions of coercive nuclear use, especially nuclear proliferation induced by U.S. nuclear threats, allowed many leaders to retain their belief in the coercive power of nuclear weapons. Therefore, they considered and even used nuclear coercion for non-vital matters. Based on the theoretical concepts of nuclear learning and using a historical analysis, my dissertation finds a causal mechanism of nuclear learning that could explain what promoted or hindered learning of the technical and political reality of nuclear weapons and led them to the counterproductive use of nuclear coercion.