Using a historical institutionalist approach, my study seeks to fill an important gap in the law, politics, and development literature by exploring how conflict states use constitutional reform to foster development and democratic transition, particularly among countries that have emerged from civil war. These include the United States, Spain, and Sri Lanka, which, in each of the past three centuries, have experienced civil wars yet emerged in a more peaceful and stable condition in the decades to follow. Despite their prevalence, there are crucial aspects of civil wars that remain poorly understood. In particular, there is a significant gap in the literature concerning the nature of legal and constitutional change in countries emerging from internal conflict. Reformed constitutions, amendments and legislation may offer meaningful benchmarks by which to assess both “thin” and “thick” conceptions of governance and the rule of law before, during, and after internal conflict. The nature of constitutional change is especially important among post-conflict states given the urgent need for a clear national vision for inclusion, reconciliation, and economic development. It is argued that in order to sustain legal change in post-conflict contexts, countries should adopt an inclusive approach to post-conflict state-building. This would mean reconciling narratives of victimhood; safeguarding autonomy and land rights in devolved regions; ensuring language parity and religious freedom; and protecting human rights; providing for inclusive economic growth. The thesis draws upon fifty semi-structured interviews with American, Spanish, and Sri Lankan historians, lawyers, judges, policy experts, members of civil society, private citizens, diplomats, and MP’s as well as survey data from national and international organizations and government statistics bureaus. It examines American, Spanish, and Sri Lankan statutes, constitutional texts, and case law from before and after their respective civil wars.