His research focuses on the interface between International Relations and Historical Sociology, and on processes of radical change, most notably revolutions. He is the author of Negotiated Revolutions (2005) and, with Barry Buzan, The Global Transformation: History, Modernity and the Making of Modern International Relations (2015). He is also the editor, with Chris Armbruster and Michael Cox, of The Global 1989: Continuity and Change in World Politics (2010).