This paper has two interrelated foci, one theoretical and another empirical. Theoretically, it examines several questions: When do passive identities become politically visible? The main interest here is to investigate how and under what conditions to social identities become political. What role do political actors play in this process? And finally, what implications does such a politicisation of an identity have on regime construction and deconstruction? These theoretical questions will form the point of entry into the politics of sectarianism in the two case studies of Iraq and Lebanon. Rooted in the social scientific tradition of Historical Sociology, this paper argues that whilst sectarianism is now too visible in Arab politics, it has been an active, but latent, socio-political factor in the making and unmaking of political regimes in the region. By systematically comparing the two cases of Iraq and Lebanon, the paper will demonstrate that the politicisation and visibility of sectarianism varies in the two cases due to various factors: (1) Different state formation trajectories; (2) varying dominant socio-political norms; and (3) different regime types. The paper shows that whilst in Lebanon sectarianism amounts to an historical institution, in Iraq the demarcation of sectarian boundaries took time to crystallise, contributing to gradual state failure. The paper divides into two key parts. The first addresses the theoretical questions, focusing on identity politics and its relation to regime making and unmaking. The second part compares the two cases by examining the three variables identified above