Historical Sociology (HS) is a subfield of sociology studying the structures and processes that have shaped important features of the modern world, including the development of the rational bureaucratic state, the emergence of capitalism, international institutions and trade, transnational forces, revolutions, and warfare. HS differs from other approaches in sociology given its distinction between routine social activities and transformative moments that fundamentally reshape social structures and institutions. Within international relations, the relevance of history in the field’s study has been highly disputed. In fact, mainstream international relations (IR)—Neorealism and Liberalism—has downplayed the importance of history. Nevertheless, World History (WH) and HS have exercised a significant degree of influence over certain theoretical approaches to the study of international relations. The history of HS can be traced back to the Enlightenment period and the belief that it was possible to improve the human condition by unmaking and remaking human institutions. HS was then taken up by a second wave of historical sociologists who were asking questions about political power and the state, paving the way for greater engagement between IR and sociology. Third wave HS, meanwhile, emerged from a questioning of received theoretical paradigms, and was thus characterized by theoretical and methodological revisions, but only minor and incremental changes to the research agenda of second wave Historical Sociology.