“…In particular, our emphasis on the importance of external threats is related to the insights of Alesina and Spolaore (), who study the role of war in shaping political boundaries. It is also related to Levine and Modica (), who propose a theory of the emergence (or absence) of hegemonic rule . In examining the causes of political fragmentation and centralization in China and Europe, we build on earlier work that points to the role of geography, such as Diamond (), and on the work of many historians who stress how the threat of nomadic invasion from the steppe shaped Chinese history (Lattimore, ; Grousset, ; Huang, ; Barfield, ; Gat, ; Turchin, ).…”