This article addresses the inadequate analysis of modern social revolutions within orthodox International Relations due both to the historical context and the trajectory of the discipline. A critical review of the literature that has more recently come to acknowledge the relevance of revolutions and revolutionary states to IR reveals a number of enduring shortcomings. The present article suggests an alternative framework for the study of revolutions by conceiving them as rooted in the dynamics of the globally dominant socio-economic system, capitalism. It is argued that the uneven global expansion of this system and its peculiarity contribute to the explanation of revolutionary upheavals in the modern world. This is illustrated in the final section of the article by a case study of the Iranian Revolution of 1979, which also challenges recent explanations of the revolution in terms of ‘Islam’ or ‘Islamic culture’.