South Korea decided to develop nuclear weapons and surface‐to‐surface missiles in the early 1970s. The Park Chung‐hee administration made the decision because of its concern about a complete withdrawal of US forces from Korea following the Nixon Doctrine. Simultaneously, increasing nationalism within the administration, caused by its tumultuous relations with the United States, further strengthened such pursuits. Later, when faced with the US threat to withdraw security and economic assistance, the administration slowed down active development of nuclear weapons in 1976, but it continued missile development. However, the Chun Doo‐hwan administration, inaugurated in 1980 after military coup and massacre, froze all weapons‐related nuclear research and the missile programme. The Chun regime made such a change because it needed the support of the US to make up for its weakness in legitimacy and because the Reagan administration provided a solid defence commitment to South Korea.