This opening chapter outlines the book’s central argument, evidence, and political economy approach. The book argues Muslim societies tend to be less democratic and more conflict prone on average. However, there is considerable variation within the Muslim world depending on how Islam was spread. Territories where Islam spread via military conquest developed institutions and practices that led to political regimes that made them more impervious to democracy and, in response to declines in rents, more prone to civil war. In contrast, societies in non-conquered territories – including some Muslim societies, such as Indonesia and Malaysia – developed governance structures that made them more susceptible to political (democratic) development; and where declines in rents provided opportunities for transitions to democracy. A central takeaway from this book is that neither Islam nor aspects of Muslim culture are the root causes of political violence in many contemporary Muslim societies. Rather, it is due to the institutional legacy of Muslim conquest and contemporary rent streams. By linking these two independent variables – conquest and rents – to patterns of political violence, the theory and empirics advanced contributes to rich literatures in institutional economics, historical legacies, international relations, and the resource curse.