This study uses an interdisciplinary approach to address the challenge of transnational threats, namely terrorism, to liberal democracies. Terrorism poses unique challenges to the liberal democratic state, and the transnational nature of terrorism necessitates cooperation between and among states. However, terrorism must be analyzed in a political and strategic context. The forces of globalization and fragmentation and the increasing claims of irredentism and secession, require a reexamination of state legitimacy. The best way for states to win legitimacy vis a vis terrorists is by adhering to liberal democratic values and cooperating with other such states. Such cooperation, which affects domestic and foreign policies, requires a convergence of political cultures among those cooperating states. This study analyzes three cases: the Basques in Spain, the ethnic Albanians in Macedonia, and the Kurds in Turkey. This study sheds light on how academics and policymakers ought to characterize and categorize terrorism, and it provides insights on the concepts of political legitimacy, liberal democracy, political culture, and political community. As the US assesses its homeland defense posture, it must resist any temptation to weaken its liberal democratic values, and as a superpower, it must encourage other states to adhere to liberal democratic values as well. Liberal democracy is not just a normative concern, it is a security imperative in today"s transnational security environment.