DescriptionRivalry has been an essential element of the human story from the inception of life to the current interconnected globalized world. The central aim of this dissertation is to observe the persistence of adversarial relations between rivals with nuclear weapons. The central questions posed in this study are: why do nuclear rivalries persist, despite incentives to cooperate and opportunities to resolve the conflict? Furthermore, what explains the variation in the interactions between nuclear rivals? And, under what conditions do nuclear rivals cooperate with one another? This research project tackles these questions by focusing on the role of nuclear weapons in rivalry interaction and termination. To understand rivalries with nuclear weapons, I employ the concept of “adversarial peace” and highlight the persistence and cyclical pattern within nuclear rivalries. The core of the argument rests on the mutual vulnerability dilemma where both sides feel a profound psychological susceptibility to mutual annihilation and perceive that the other controls what the state values the most. In this way, strategic rivalries with nuclear weapons transition into a state of perpetual adversity. To test this argument, I employ a historical approach with a focus on the individual, regional and system level factors through in-depth historical case studies. My main cases are the US-USSR, and US-Russia and the India-Pakistan, and a mini-case study of Brazil and Argentina where the nuclear question was resolved and a protracted rivalry terminated.