In his new book, Civil Wars: A History in Ideas, David Armitage reports that the world has shifted from the era of wars between states to an era of wars within states and that such wars are longer, more likely to recur, and wreak more destruction than the wars that preceded them. What makes a war "civil," and what do the trends in civil wars portend for the future? We will explore these questions and more as we grapple with the roots and dynamics of civil war. David Armitage is the Lloyd C. Blankfein Professor of History and former Chair of the Department of History at Harvard University, where he teaches intellectual history and international history. He is also an Affiliated Professor in the Harvard Department of Government, an Affiliated Faculty Member at Harvard Law School, an Honorary Fellow of St Catharine's College, Cambridge, and an Honorary Professor of History at the University of Sydney.