How do states use threats to shape the behavior of their adversaries, and how do resolve, commitment, and the availability of different diplomatic tools shape the effectiveness of those threats? In this talk, I outline a research agenda that develops a unified theoretical framework for deterrence, emphasizing how the scale of potential challenges interacts with instrument choice and strategic commitment to shape deterrence outcomes. Across a series of formal models within this framework, I show that greater resolve does not always strengthen deterrence; that deterrence failures can be driven by the defender’s ability to choose among different diplomatic tools rather than by simple breakdowns of credibility or capability; and that combining constraining measures with threats of retaliation can fundamentally alter deterrence outcomes. Together, these results carry significant implications for how we understand the logic and limits of deterrence, for how reliable deterrence can be across different strategic environments, and for how deterrence effectiveness should be assessed empirically.