Existing scholarship suggests terrorism is an ineffective method of political contestation; groups rarely achieve their political objectives and are often disrupted by the security services. These findings invite us to look again at the dominant rational choice paradigm, which suggests that terrorism is selected as the best strategy to achieve predetermined goals. Unpicking the assumptions underpinning this model using historical case studies, comparative analysis and typology development, this thesis broadens our interpretation of what those who use terrorism seek to achieve. It does so via a tripartite framework. First, employing a new reading of American pragmatist thought, interpreting militant group goals as culturally and socially mediated problems opens up a new vista of outcomes, in particular examining the way terrorism seeks to change relations between people. Second, using Social Movement Theory as its organising framework, an empirically derived typology of militant groups sets out the background political conditions and organisational characteristics of 28 dormant groups. Using existing models of interpreting outcomes to assess these historical cases demonstrates the unmet challenges of providing robust explanations for why terrorism ends and what it achieves. Third, the thesis explores the promise of a mechanism and process-led approach to explaining outcomes. It does so through in-depth examination of two historical case studies: Kach and the Aden-Abyan Islamic Army. Despite being classified as failures, using largely neglected primary sources, the case studies reveal a range of fascinating and important outcomes that still resonate in Israel and Yemen today. Most of these methodological and conceptual tools are being applied to the question of terrorism's outcomes for only the first or second time. In doing so, this thesis offers greater depth than existing scholarship on how terrorism ends, by looking beyond measures such as success and failure in interpreting outcomes, whilst affording greater breadth through its ability to make comparative assessments at the level of mechanisms and processes. The result is a more detailed and robust set of explanations as to how terrorism ends and what it achieves, illustrated through detailed historical case studies of two interesting, yet often neglected, groups.