This research examines the international relations between North Korea (the Democratic People’s Republic of Korea or DPRK) and Iran in the context of their shared perception of a threat from the United States. We discuss the conventional idea of the international relationship—the enemy of my enemy is my ally—to explain Pyongyang–Tehran relations, evaluate its past and current relations, and offer policy suggestions for the recent denuclearization approach toward North Korea and Iran. Using newly discovered archival resources and political records, we challenge the conventional idea that the two states share the same threat perception in a consistent manner and suggest the level of their military cooperation changes depending on the approach from Washington and the international community. This research provides a more exact picture of the international relations North Korea and Iran since the 1980s and of the link between their shared threat perception and denuclearization debates.