This dissertation aims to explore the origin of the current 'nuclear divide' in the Northeast Asia in which US allies do not have nuclear weapons in contrast to nuclear-armed non-US allies. Taiwan and South Korea were motivated to develop their own nuclear weapons in the 1970s under the hostile security environment in the region and the fear of being abandoned by their patron state, the US. However, they failed to reach their original goals because of strong US opposition. Thus, this research, based on extensive archival research, will attempt to examine in detail how the US was able to dissuade Taiwan and South Korea from pursuing their nuclear ambitions.